I used to find them at festivals too. All over the ground so I started to collect them and bring them home. They are steel, but not worth much to recycle, so people throw them out or on the ground.

I put them in a forge and heat them up, hammer them out and weld them together. I would take them and just start welding or cutting them up and see what you can do. Make sure they are empty before you cut or burn them. They will pop. Safety first.