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.