Hm...
-wallet (contains driver's license, bank card, student ID, ID, insurance card for hospitals, member card of a shop, BahnCard (card from Deutsche Bahn, you get 50% off every trip if you have one), MensaCard (replaced money in our cafeteria, money of course, packstation card (a service from our mail company - you can fetch packets everytime you like at one of these) and band-aid)
-iPod touch with SH IE6
-mobile phone
-a pen
...is what I usually have with me
On trips I add:
-a book and/or a magazine
-bottle of water (1l)
For university I take along:
-glasses (I only need my glasses to read things from a certain distance)
-notepad (too slow with a keyboard)
-bottle of water (1l)
-a magazine (only when taking the tramway)