Recycle those caps into all sorts of buttons.
I've been testing different ways of making buttons from bottlecaps and I've found the best way, finally. It's actually really easy and I don't know why I didn't come up with this method any sooner.
Btw: I used polymer clay with my buttons, but you can do whatever you like. Felt works great and gives a softer look :D. I gave a hole bunch of felt buttons to my aunt when my little cousin was born.
Now you need to punch a small V-shape in the middle of the bottlecap. Put your screwdriver on the bottlecap and hit it with your hammer to do this. This could take a little more effort. A screwdriver is also not really made for this purpose, so if it breaks or something (unlikely, but still) it's your own risk. You've been warned.
Push the V-shape out so it stand up on what will be the backside of your button, you can decide which side that'll be.
Now you can decorate the button. I used polymerclay. The bottlecaps can stand the oven fine, so you can put the clay around the edge of the cap if you want. You could decoupage it, cover it with fabric or anything else you can come up with. Don't forget to add any protective layer if that's possible!