Well, being the expert fireworks trader that I am, having traded many fireworks pins, I can tell you some things you could probably get.
Retired pins, including submarine and lion, maybe a couple depending on the person.
Quest items, usually furniture or pins. I've gotten train teleporters, wanted posters, saddle couches, rocket couches, a heartless hamper, an ace with the hole rug, cactus chairs, Retro pins, and some other stuff. I was even offered one of the new quest pins.
Clothing, such as black and gold ears, and even a tiara and princess dress. (Don't ask).
What you probably won't get for one fireworks pin:
Sorcerer ears (unless the person is extremely nice and generous)
Teleportation
Inferno
Pirate Quest stuff (it's just too new and still too rare.)
Hope this helps.