All sorts really. I'm happy shooting chained bands, flats, looped or single tubes blah blah. At the moment I'm playing with 4070 tubes "tied-down" on a simple natural for pebbles and marbles.
Attachment method like this, but using tubes not squares:
Just put the rubber against the fork, once round that with a strip of cloth, then loads of wrap-and-tuck TBG or rubber bands. You pull back against the attachment rather than over the top. Shoots really well with marbles and small stones. Not killed with marbles yet but judging by the mess they make of a bean tin I think it's more tha