I kept a small army of monkeys, a few organs (have a room called ugly organ- figure I may get in trouble for that one day lol that used to be full of organs but sold those), papered a few rooms with posters- and save all of my chests- I used close to 100 building my waterslide ride...
I do wish they'd be tradeable I have a friend who adores the monkeys and would gladly store as many as she could and as I was selling them back last night she was fussing with me and I told her if I could trade them over I would but until then at 5 credits a pop they are getting sold.