Other than the coins that several people have mentioned, I'd add a bandana (back pocket) and a couple of pieces of hard candy. The bandana serves multiple purposes, from triangular bandage to blowing your nose. While the hard candy won't replace water, sucking on one can make you feel less thirsty, and gives you a little sugar rush. I'd go with the sweet kind, not the spicy kind.

Carrying water is tough. You might want to think about adding an empty baby milk bag to carry water if you need to.

Otherwise it seems like a pretty well thought out kit.

Kevin B.