Tylenol makes a tube for their 10 caplet sample packs that is about 5/8" wide by 2 1/2". As it's packaged, it is about half full. You can get 6 generic Aleve, 4 of the Tylenol, 6 Ibuprofen, and still have room left.

I haven't tested them for water resistance but I usually tape the top w/ electrical tape

They are also a good size for carrying a spare CR123.