Have a portable gas burner and thus the butane cans for it.  Once they're finished, what's the appropriate way of disposing them?  There might be the tiniest bit left in there and I don't have a puncture tool so I obviously don't want to just throw them away.  Would the place of purchase take them back?

 

Thanks

They are very low pressure so there's really no hazard in bashing a hole in it with a large nail. Then just put in the regular trash.

 

Put the nail through a piece of wood if it makes you feel safer (and you gain a handy self-defence weapon too).