How many compressed gas cylinders do you have?

I have a few hand-help propane other gas cannisters, all empty. What does one do with them?

We have oxy/acetylene, big noisy compressor, BBQ Propane, Big-ass Propane, 4-5 Fire Extinguishers, uncountable lubes, solvents and paints etc. in rattle cans.

The oxy/acetylene is secured to the welding cart rig, and the compressor has an enclosed wooden area in the garage. The big-ass propane is secured by gravity behind the house. One fire extinguisher stays in the kitchen. The rest is allowed to wander at will.

Nothing bigger than a 20lb propane for the grill, and I have yet to fill it this year.

I do have a E36 M3 load of small empty propane bottles, a mix of 1lb camping cylinders and benzomatic torch cylinders.