what cristeen said
I use a heavy drinking glass or mason jar in a metal bowl most of the time. When those are missing, I've used a klean kanteen in a glass bowl. The main thing being that one of the surfaces, should you pound too hard, is able to bend out of the way, (never had it happen, it's a theoretical safety precaution, but glass on glass/ceramic does see unsafe) rather than cause it to shatter or chip all over your cabbage and hands and such.
By putting the salt on first, it starts to pull the juices out of the cabbage right away, so as you pound, more juices are drawn out more efficiently. It always ends up being enough liquid to cover, when I really pack it tightly down into the mason jar. and then it floats up again, but that's fine, I push it down the first few days, and then ignore it.
(also, I usually multi-task the pounding. reading, watching tv, reading mdc, while I do. if I had munchkins old enough, I'd outsource it to them.)