This is a quick and easy project to build a portable Raspberry Pi computer that fits right in a lunch box. It's a good first Pi project since it requires no coding, soldering or tooling of any kind. All you have to do it acquire the parts, plug everything in and secure it in the lunch box.
The Raspberry Pi isn't a very fast machine, but it IS extremely versatile and easy to use. This rig will have all the functionality of a wifi netbook, if a slow one with a very small screen.
There are lots of ways to do a project like this so feel free to deviate from my plans. All of the parts are modular and you can change its abilities a bit by using different parts.
EDIT: While I used a Raspberry Pi model B in this instructable, I would advise folks to use the Model B+, it uses less power than the Model B which sometimes can't run both the Wifi and Bluetooth dongles.
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Step 1: Parts List
Here is the list of parts I used. Please note, these are the first one's I found for each item, if you shop around you can probably pay a bit less. Also, feel free to swap out components, like different size batteries or screen. All of the bits are modular.
Custom Lunchbox $6.50: http://www.lunchboxes.com/Custom-Lunch-Boxes-p/cu...
10,000 mAh USB Battery $50.00: https://www.adafruit.com/product/1566
Raspberry Pi Model B+ with preloaded SD card OS $35: http://chicagodist.com/products/raspberry-pi-mode...
Raspbian OS Micro SD Card $12: https://www.sparkfun.com/products/12998?gclid=Cj0K...
Clear Pi Model B case $10: http://www.ebay.com/itm/like/281391676058?lpid=82
Composite 5" LCD $26: http://www.aliexpress.com/item/Free-shipping-5-Hi...
AZIO Bluetooth Keyboard $30: http://www.bhphotovideo.com/bnh/controller/home?g...
6,800 mAh 12v Rechargable Battery /w charger $20: http://www.dx.com/p/1268-12v-6800mah-rechargeable...
1 Micro USB Cable $1: http://www.wholesalecables.com/ProductDetails.asp...
Edimax Wifi Dongle $10: http://www.kmart.com/edimax-computer-edimax-150mb...
If Using Pi Model B: RCA adapter (male to male) $4: http://www.amazon.com/RCA-Male-to-Adapter/dp/B000...
If Using Pi B+:3.5mm to RCS cable $6.30: http://www.rakuten.com/prod/skque-audio-video-cab...
Note: The Pi Model B and B+ use different composite video ports. The B uses a traditional RCA jack, and the B+ uses a 4 pole 3.5mm jack that outputs video and stereo sound.
Total Price $200 + shipping with these items.
Step 2: Putting It Together
As for the How-To, it's pretty easy:
1. Charge both batteries, the 12v comes with a charger, the USB charges from any USB chargepoint
2. Put the Pi in it's case
3. Put the Pi's SD card in it, this is your OS and storage
4. Plug the dongles for the Keyboard and wifi into the Pi
5. Use the RCA adapter to plug the screen into the yellow port on the pi
6. Plug the 12v battery into the screen
7. Plug the USB Battery into the Micro USB power jack on the Pi
Once you plug the power into the Pi it will boot up. Check it out, make sure everything works. You might need to configure the wifi dongle or change the screen size. If it defaults to a res that is too high it'll be hard to read the text, so you can always plug an HDMI monitor into it while you configure it. I won't go into the details, there are a TON of easy to follow Raspberry Pi tutorials on the web.
Finally, once you know everything works, use some foam tape to mount everything in the lunch box. I only used tape on the front edge of the keyboard so I could swing it up to turn it on and change it's batteries. Make sure that you arrange things so you have room to get into it to charge stuff later and also make sure there is room to unplug the Pi when you are done using it since the Pi doesn't have an on/off switch.
That should cover it I think. Good luck and have fun with your lunchbox computer!