A Nalgene water bottle makes an inexpensive waterproof first aid
kit on shorter trips. To save space, wrap lengths of waterproof
adhesive tape around a plastic film canister so you can leave
the original package at home. Pack the film canister with a few
assorted medications -- trim blister packs or separate pills in
small sealed plastic bags -- or whatever else might fit inside.
It's a bit harder to get things out of this kit, but it's
inexpensive and works!