In the spirit of John Gould's How to Camp Out, I present to you some things you may require if you ever find yourself on a nerdy expedition to, say, What! The! Hack! or something similar. 
DECT phones. These are stunningly useful.
Lots of ethernet cable. You'll never know when Ethernet cable will be handy. Wrap the cable itself with gaffer tape (duct tape for you Yankees) and cover the ends and it can double up as a poor man's belt. 
"Programming Ruby". If you get stuck on public transport, you might as well use the time to learn a new programming language. And why not a really sexy object-oriented language like Ruby?
Spare batteries. You'll find plenty of uses for them.
Wireless gear: routers, hubs, Bluetooth crap. All of it can be used for neat stuff. Especially useful if you've got lots of money and access to the 'net on your phone.
USB extension cables. You'll always need them.
Recordable CD's and DVD's. Do I need to spell out why these are useful?
Friends outside. Getting your data out can be an arseache when in the field. Make sure you've got a buddy with skills, a decent connection and some hosting space, as well as a degree of trustworthiness. Just in case, you know, you bump in to the living, breathing Elvis working on a wifi mesh network.
Google via SMS. If you're in Europe, you can text Google queries to 6GOOG (64664) for your standard network charge. This can get you out of some sticky situations. For more advanced stuff, have a friend a text away with Google-fu. Similarly, if you need good advice, know some online places to go where you can get advice without big bandwidth or cost.
If you've got advice, blog it and send me an email.
