In the shallower molds, I've been using polymer clay and paper clay to make pendant shapes, (and then embellishing with paper or other stuff and clear-coating). It's a bit tough to get the polymer clay ones out so I leave one side or piece with a long tail. And definitely sprinkle baby powder or corn starch in mold before pressing in anything.
Thanks a bunch! I do have quite a bit of paper clay. Some of them, though, I was hoping to encase stuff in (the jewelry shapes). I don't think liquid Sculpey would do the trick? =/