From what I can tell, the only shop items you can currently trade with other players are subscription tokens. But wouldn't it be kind of nice to be able to trade the limited time hats? It would be nice for people to be able to get the hats even after they have left the shop.
Other tradable items would be fun, too. How about special limited time seeds that would grow rare crops or special paint to change the color of your house? I'd like a pretty pink house.