Here is the trick with a mini hammer, having carried a tool kit like this on a Harley chopper for years. Get a small hammer like a ballpeen with a wooden handle and simply cut the handle short enough to fit in the kit.
Took your advice Cary and got this mini, 1 ounce ball peen hammer and shortened the handle. Not sure if it would do much outside of very small nails but I have a hammer! (Isn't that a song? If I had a hammer...... )