I carry my lunch, a change of clothes, wallet, keys, passkey for work, mobile phone, Palm Pilot, mp3 player, my lock, water bottle, some toiletries and a hand towel for shower/cleaning up when I get to work, as well as my meager collection of bike tools, mini pump, tube and patch kit. Rear blinkie on back of bike, headlight for front (will use/carry once it gets darker earlier). All other items crammed into backpack (but this and this are on my Amazon wishlist... how much nicer miy ride could be with these!)