I need to create an inventory some day. I have quite a few boxcars, but I might actually have more Cabeese than I have locomotives to pull them (Note to self get more locomotives). I also really like Weaver's PS-2 2 bay covered Hoppers, which I have a lot of. The other one is Lionel's 9333 flat car with Southern Pacific trailers on them, for some reason I really them and buy them whenever the price is right, those are something that I really do need some locomotives for. I would LOVE a Legacy set of Black Widow F-7s, but they just aren't in the budget in the foreseeable future.
I have a pretty good mix for the other cars though, I definitely like Stockcars more than most it seems, probably 6-8 of those, but when Union Pacific Steam is your main interest, some stockcars are mandatory.
I could do with a few more gondolas, but it is Tanks and hoppers that are most in need of being added to the roster, some but not enough(unless of course, you ask my Wife, She thinks that I have too much of EVERYTHING already.
Doug