Ok, I have a very nice messenger bag (or a man purse as my wife calls it) - like this. I don't like the feel of it when it's empty, so I'm packing it up with an "every day (nerd) survival kit". This is something that I'll be carrying with me all the time so I don't find my self unprepared for any situation (so I guess that makes it a man purse). Here's what I've come up with so far: multitool (of course). Swiss Army knife or Leatherman style. Or both. Probably both. duct tape (small sized roll) small roll of electrical tape, too zip ties travel sewing kit dental floss (not for my teeth, but it's an amazingly handy way to pack pretty strong string - I've sawed through 1/4 plastic with floss before. Don't ask.) Small flashlight AA and AAA batteries USB Dock cable standard mini-USB cable USB to AC charger Spare cellphone charger (I can save space here using the USB cable for my Palm and the above USB to AC adaptor) blank DVD/CDs USB flash drive (actually I'll be super efficient here and pack a 2gb microSD card in a tiny USB adaptor, and my microSD to SD adaptor... I'll be able to plug the card into any PC, my/most digital cameras, and my/most cellphones, too) Digital camera (about to get a Nikon D40, but it's pretty small, so it'll should still fit even with a smallish case/wrap around it) Cellphone/iPod (though those are usually in my pockets) ziplock bag with: travel toothbrush, toothpaste, deodorant, hand sanitizer, "wet wipes", and some extra, empty, ziplocks .5L bottle of water (if it gets too full this will be the first to go. Water is heavy/dense, but I'll keep an empty bottle for refilling when thirsty) couple of energy/granola/candy bars gum/mints So, what am I missing? What's the one thing you couldn't get through the day without that's not on the list? I'm considering putting a spare ATM card (not debit, since ATM cards NEED a PIN to work so if it gets lost it is less of a risk), a $20 bill, and some secondary form of ID (it's illegal to have two copies of your drivers license, so I'm not sure what else might do me some good).