This is the third year that I will be carrying one. I've gone through several different bags, the one I have now is a good balance of size and portability. I got it at a local military surplus store so I can't recommend looking for this exact bag, but I'll discuss why I like this one.
I'll also be deconstructing my bag and rebuilding it with some new ideas that I got from looking at the survival kit instructables.
Aside from having the resources in this bag at my disposal at all times, it also helps me to not forget things because they're all in one place. I usually don't loose my keys, because they go on my Possibles. I don't loose my phone because it's in my Possibles. I have on occasion misplaced my Possibles, but it's kinda big and not easy to miss.
Step 1: Don't Call It a Man Bag
In order to intellectually distance my possibles from a purse, it does not have a strap that goes over the shoulder (it originally did but I took it off). It has a carabiner that hooks to my belt, pants or pocket. It works just as well, maybe a little better because a purse strap puts uneven weight on one shoulder and actually hurts after a while. Hooking to a belt doesn't seem to have the same negative effect.
What I like about this bag
It's relatively small and light.
It substitutes for a wallet.
It has a number of different sized pockets that are suited for medium to small sized items.
It has two sturdy D rings on the sides that make hanging things off it and hanging it practical.
It's exterior is very sturdy and has held up under everyday use.
If you can find a bag that does those things you'll do well.
What I don't like about this bag
It can be complicated to open and get to things in the deep insides.
The belt loop is vertical instead of horizontal. I would use the belt loop if it were horizontal.
Some of the lining is all that holds things in the top pocket and has fallen apart. (Fortunately my wife is a skilled seamstress.)
Step 2: Balance Size and Use
My truck (frank) is technically my other Possibles but he weighs 7,400 lbs and is very thirsty so I don't take him everywhere.
Mini Can Be Good Enough
If you're not sure how often you'll need an item, try the smallest version of it that you can. If you find that you're using it all the time and you think a larger version will work then try moving up. Examples would include flashlights, spools of string, rolls of tape etc. Sometimes moving up a step in size doesn't work. A bigger notebook would work better for me but wouldn't fit in my pack so it's impractical.
One way to keep weight and size down is to to carry as many multipurpose tools as is practical. Now when I say multitool, I'm not just meaning my Leatherman. I carry an iPod Touch and it rivals my Leatherman for how much use it gets. If I had the money I could combine the iPod with the Phone and further reduce my load but for now it's better this way.
Instead of the glasses case that I settled on trying for holding small items, I think an Altoids can might be better, mainly because it could be put on a fire to cook with (or boil a small quantity of water). I would then have to replace the tin, but it would be possible that I might want that ability. The nice part about that is it would not take up more room so that added ability does not cost more space.
Form can be very important
How an item is shaped, or how the item fits into your possibles makes a big difference. For instance. I have a flashlight that I can hang off the other D ring of my bag (the one that doesn't have the carabiner) so I always know where it is. It can't sink to the bottom of the bag or be shoved in the wrong pocket. But it's not very bright, so I have a led hatlamp that sits in one of the back pouches. It's a decent flashlight and I usually wear a hat so it works great, but it doesn't clip to the D ring so in a pinch, when I need a flashlight, I go for the one I can get to the easiest.
This kind of redundancy is bad for my possibles overall but here use overrides the volume the two flashlights take up. In other words, I'm still looking for that perfect flashlight.
Step 3: Ease of Access
Out of sight, out of mind. I frequently forget that I am carrying things that I could be using if they sink to the bottom.
Implementing this is obviously going to depend greatly on your choice of bag.
With this in mind, I thought about putting small items in an Altoids tin in the big pouch of my Possibles. Unfortunately I don't have any Altoids tins. So I decided to try a glasses case that I had. This makes the case removable and prevents the little items from being lost in the depths.
The main idea there is to take smaller items that are difficult to find and retrieve and make them easy to find by putting them in a container that can be retrieved and then searched.
Step 4: What I Carry Now
In the front pouch of my Possibles is my Leatherman and my phone. I can take these out without opening anything.
Inside the front flap is my ID, store cards, etc. My bank cards and cash go into a zippered pouch on the side. I also keep a pen for everyday use in spot made for that.
In the main pouch, I keep a Moleskin notebook, my sling (that also could be harvested for it's string), my checkbook, a flashlight (hooked to the other D ring) and my iPod.
Stuff that got shoved to the bottom of the main pouch includes my sling, my headphones and a few more pens.
On the back is a small pouch that is good for small items. I keep needle and thread a usb drive (not shown) and a spool of thick dental floss.
Then there is a skinny but deep pouch that I keep a hat mount flashlight, a positionable dentist mirror (that I don't use so it's going out) and a magnesium fire starter.
Step 5: Small Touches
One of these things is that I put a quick disconnect between my car keys and my other keys. The reason for this is, when I lock the door to the house, get in the car and start it up, someone (sometimes me) remembers that they left something in the house. I got tired of turning the car off (especially in the winter when the car could be warming up) and taking the keys out to unlock the door.
Secondly personal and business cards are great ways for people to not forget your name or how to get ahold of you. Personal cards seem kind of dumb at first but wouldn't it be great to hand them out when you get a new phone number or email address instead of having to write it down for a hundred (or more) people?
Step 6: Reevaluate Your Possibles
I started to notice I was using my iPod for notes instead of my Moleskin. I do occasionally use the notebook, but not enough to justify carrying it everywhere. I'll just leave it in Frank.
I was then looking at the survival kits and wondering if I could incorporate a few ideas into my possibles.
In the next month or so, I'll know if these things are worth carrying every day. If my stock of them depletes quickly, then that's a good sign.