I've worked and traveled overseas on a number of occasions, and I've never found a truely satisfactory checklist to follow.
I've spent YEARS in places as diverse as post hurricane Puerto Rico, Afghanistan (both on military bases and on the economy), Iraq (on the economy; NEVER DO THIS, NEVER!), Kuwait, and the Philippines.
Step 1: The Obvious Paperwork
1) Have a passport with MORE than a year left on it. I recommend at least 3 years as renewals in goshforsaken-stan is a major pain (mine involved 3 helo flights, 2 convoy rides, and 4 MONTHS!). If you are getting a new one, GET THE EXTRA PAGES; lots of countries amuse themselves by blowing an entire page of your passport for their "transit visa" every time you pass through. Copy the title page and stash it separate. Because if you lose your passport it can't hurt...
2) Make sure your passport doesn't have any stamps/ visas that could get you in trouble. Some of the Muslim countries will look askance (or worse) if you have Israeli stamps in there.
3) Make sure that you don't have any outstanding visa issues. I traveled THROUGH a country and they failed to record my exit in their database; I got ARRESTED and spent the long night in jail for "overstaying a visa" when I returned 5 years later. Not fun. Not exactly a "Midnight Express" kind of experience, but still...
4) Check the US State Department website for travel advisories. AND make sure you have all the advised inoculations. GET a copy of your immunization record to tote along with you. DON'T believe them when they say "Oh, you can just use the electronic version and skip carrying the yellow card around..." Truly they lie. GET THE YELLOW CARD!
5) Have a copy of any needed prescription(s) and eye glasses numbers. Stick these with a copy of your passport title page & yellow card. SEPERATE from your passport.
6) MONEY. You need some hard cash. Be prepared to blow it if you REALLY need to get onto a flight/ ferry/ whatever by bribing someone. I carried at LEAST $5000 in cash at all times in Iraq. And $1000 in Afghanistan. And YES, there are times when a few thousand in bribes out of your pocket is the least of your problems. Consider a money belt.
Step 2: How You Pack
You need to understand, up front, that there are 4 kinds of stuff you have.
1) Stuff that is life or death all the time. Your passport, money & 1 credit card, pocket knife, cell phone, and life saving drugs (like an Asthma Inhaler, Epi pen, etc) ALL this stuff is carried ATTACHED to your body all the time even when you aren't in immediate danger.
2) Stuff that is pretty darn important in certain cases. Like a seatbelt cutter if you are travelling on MRAPs.. This stuff is carried readily available as appropriate (the seat belt cutter should be on your body armor, for example). I tended to carry a good fixed blade knife, first aid kit, water bottle on my body armor. Basically this is a special set of stuff carried attached to your body.
3) Stuff that is important for comfort and work. This can include your laptop, dopp kit, one pair spare socks. I tend to include a leatherman "micra" too. A warm jacket is often a good idea. All this goes into your small pack/ shoulder bag/ man purse...
4) Longer term stuff. This is your clean shirt and pants, sleeping bag or blanket, etc. This goes into your roller bag. Note you are packing for a couple to 4 days. Wash stuff in the showers if needed. Better the washing pain in the butt than dragging around WAY too much luggage.
5) Everything else. You can ship it and it gets there (or not) whenever it happens to get there.
REMEMBER, this is working overseas in an austere environment, NOT a time when you should be worrying about fashion...
Step 3: Clothes
Go head to toe when you think about what you are packing/ taking.
Hat. A good one, like a Tilley, is indispensable. So much so that I ALWAYS have a spare in my main gear bag/ footlocker back at home base. If you are going to be working outside somewhere where it's bitter cold AND blazing hot, you might want to have hot and cold weather hats. Afghanistan comes to mind...
Gaiter. This is basically the neck of a turtleneck sweater. But longer and more versatile. Also called a "balaclava" but most of those are more form fitted to the entire head/ neck and are not as versatile. You can spend a mint on a wool one or get a cheap one... My wool one lasted 4 winters in Afghanistan.
Shemagh. This is the all purpose scarf that many middle easterners (and Afghans) use for all kinds of weather. Aka the Keffiyeh / Des Mal, it can be used for lots of things. Try to not embarrass yourself with a too gaudy pattern.
Shirt with long sleeves. Generally speaking you want one with pockets. If you wear it over another shirt it doesn't have to be washed every day. So you only need a couple of these. I like the kind with the buttons to hold up the sleeves when rolled.
Long and short sleeved tee shirts. I tend to have some short sleeved tees and substitute turtle necks when it gets cold for the long sleeved ones.
Belt. A good quality one. As wide as will fit through your belt loops. I prefer leather but there are good ones of "webbing" that others swear by. You SHOULD, unless you are an office bound person on a base, have a belt pouch of some essentials.
Pants. Cargo pants are probably better than jeans for most uses. Tan pants are cooler in the summer than darker colored ones. Nylon might be preferable if you aren't flying in helicopters or working around welders all the time...
Socks. I like the wool ones you get at camping stores. In any case, don't be a cheapskate and get crappy ones that are uncomfortable.
Boots. Get the good ones. I tend to prefer Redwings if I am in a work zone (Like a MRAP repair shop or construction site) and Keen boots if I'm not. SPEND the money to get the most comfortable ones! Well worth the $150 a great pair will cost you.
Boot liners. I think the regular ones you get at the Redwing store are the best deal. The "soft" ones, like "Dr Scholls" are about useless. And the special custom ones aren't any better than the regular ones in my experience.
Gloves. Get some good quality ones. I prefer mittens (because I don't use tools all day) but in any case warm is MUCH more important than stylish. I usually wore either the "glove liners" (wool gloves) I was issued or the LLBean mittens I invested in. In case you didn't know, mittens are MUCH WARMER than gloves because your fingers warm each other. Really. Ask any Yankee.
Step 4: Extra Stuff
POLARIZED glasses. I'd recommend you get good quality polarized glasses (safety glasses if you are around tools etc) like RayBans. AND invest in some yellow lensed "shooters glasses" as well. Because in sandstorms, mist, snow, yellow is better if the light isn't really bright. If you are concerned about wearing $150 Raybans (or MUCH more for some) consider good quality second tier glasses like Sunskis or Triple Graces which have polarized lenses.
Pouch. For the misc stuff you should have. Like camera, cell phone notebook, ink pen, etc.
Leatherman (or alternate brand) tool. IF you will be traveling in a war zone you ALWAYS need to have a blade on your person whenever you travel JUST IN CASE you need to cut seat belts. Some people actually have a special seat belt knife attached to their body armor for JUST that purpose. I think you ought to have at lease SOME kind of pocket knife. I used to wear a fixed blade whenever I was off base in ADDITION to my my Leatherman.
Notebook. I like the "rite in the rain" kind, but Moleskine makes nice ones too.
iPod or equivalent. With some good earbuds that also can act as earplugs for those noisy C130 & Helicopter rides.
Decent pack. I prefer a small ruck that has no frame and is the right size to be a "carry on bag" onto a commercial flight.
First aid pouch. If you have body armor it gets attached to that. Contents will be in another step.
Step 5: First Aid Kit
IF you are going to be wandering around in a war zone or other insecure location you need a first aid kit that is ON YOUR PERSON all the time you are outside the secured perimeter (like those convoy rides and helo flights).
1) Something to stop bleeding punctures (like bullets). This is where a "combat gauze" can be crammed into the hole. Some of my Special Forces friends swear the use of a new tampon is PERFECT for this. "Qwik Clot" is great but requires you cram it in there manually and it hurts (burns). If you have a bullet hole in you your big problem is the bleeding bullet hole(s) and not the ouchyness from your bandage.
2) Something for huge gashes. This is a big bandage. I just carry a second "combat gauze."
3) Something for amputations. Get the new, store bought, tourniquet. And have someone show you how it gets used. It's not that intuitive that you can fake it in a crisis. Most military clinics will GIVE you one of these if you ask.
4) Some little bandaids. Maybe a foil pack of 3 in 1 ointment. And a roll of medical tape.
5) Some rubber/ latex gloves.
There is a lot more you can carry, but the above is a minimum for a first aid kit on your body armor.
And you probably should have a "trauma bag" available in the car/ truck/ office if you are working in the third world. Becasue help might take a while getting there.
By the way, the pics are to remind you that 1) Bring your own bumwad/ baby wipes (the locals and third world contract workers don't use it AND they stand on the seats!) and 2) you may have issues with getting your stuff washed in a timely manner. Be prepared to wash it in the showers & dry it from "paracord" stretched around your bunk.
Step 6: Luggage
You need three kinds of luggage:
1) The carry on. This has stuff you need all the time. Like a warm jacket (it gets cold on some flights), your meds (like my allergy pills), iPod, earplugs, sunglasses in a case (or they get beat up), cell charger, iPad (or just a thumb drive to store vital files) etc.
2) The roller bag (some like a big ruck for this). Clean clothes, dopp kit, laptop, etc.
3) Shipping boxes/ crates. I prefer "gorilla boxes" foot lockers (or the equivalent). Cram them with just under 70 pounds of stuff and US mail them to a APO box. They get there when they get there. DON'T pay for airmail; it doesn't really get there faster if you are using the APO/ FPO mail system. All of them go on the same planes...
Speaking just for myself. I'd rather pay $50 to ship a heavy footlocker than drag it through a half dozen airports for MILES enroute to my new home...
Note that in this pic I am wearing TWO rucks, one is for me and the other is JUST my bedding (since I was going to a FOB without provided bunks/ blankets/ sheets