Nothing yet. I haven't seen any more mouse activity in the last couple of days since I discovered the stuff in my trunk. Nothing in any of the traps yet either. I also thoroughly cleaned out all the stuff that I keep in my trunk (toolbox, etc) and saw nothing in there.
I'm going to guess that the mouse (or mice) got in while I was parked somewhere, made themselves at home for a bit (complete with nests), and left. I'm thinking it was probably more than one, since I saw evidence that they'd been in both the trunk and inside the glovebox. My back seats are the ones that can fold forward and made and open up into the trunk, so I don't find it hard to picture a mouse squeezing in and out through there.
Maybe the little shits will stay gone now.