It's been done, actually. In the spring I went to the local sports equipment store with Number One Grandson to outfit him for the summer soccer league. We were looking at water bottles, and I noticed one labeled "Emergency Kit". Packed in the bottle was a mini flashlight, a whistle, bandaids, a small compass, some string, a mylar emergency blanket, and a few other goodies.

Not a bad idea, until you need to use the bottle for water, at which point I guess you fill up your pockets with everything else.