Maybe everyone already does this for hot weather riding...I fill my water bottles 3/4 full and pop 'em in the freezer. When I go for a ride, I top off the bottle with cold water. Stays pretty cold even in a DC summer.

I carry Bactine wipes, wet wipes, and bandaids in different sizes in a ziplock bag. (Have one in my car, too.) Even if I'm not carrying a fanny pack or handlebar bag on a ride, this is something I can slip in a pocket, especially if I'm riding with kids. They are SOOOO much easier to calm down when you can mop up the blood!

(Great thread; wish I had something truly great to contribute!)