[louter]

Looks to me like they were huffing.
Usual choice is silver or gold spray paint, due to the higher content of whatever chemical gets you high.
Although it looks like black paint here.
Simple process of spraying the paint into a bag, then inhaling the fumes for as long as you can from the bag.
Sort of like using a bag to stop someone hyperventilating.
Just a guess, but that sure is what it looks like.

Thanks for the post!