I just snagged a nice camelback backpack for $5 at a thrift store.
(ive never priced them, so i dont know how good of a deal this is.)
This is a little thing just big enough for a water bottle and some sandwiches.
-or a nikon n80 with a 70-300 zoom lens =]
Seriously, this will be good for biking or when I take walks and dont want to have a bulky regular size backpack.