Don't let used fuel canisters accumulate in the garage, even if they do remind you of all your great trips. Recycle them. Most fuel canisters are steel and can be recycled along with your Dr. Pepper cans. Just burn off any residual fuel and puncture empty canisters before recycling. (We crush spent canisters with a large rock.) Coleman, which makes Powermax aluminum fuel canisters, includes a Green Key puncture tool with compatible stoves. In Boulder, Burlington, and other eco-conscious towns, you can just toss empty, punctured canisters into your recycle bin. Call your local Public Works Department and ask about rules in your area.
Different cities have different rules for recycling your used fuel canisters