I've been finding a lot of this little purple bottles named "One of the best fireworks ever" while hunting and I'm just wondering what in the world they are for?

just a gimick the EA team added to show off some graphics in kingdom Reborn. They are pretty useless, since all they do is make a pop sound when you double click them. Useless items are added to UO all the time for a short period, many of which are rares now since a lot of people did not collect them. I would suggest you get one of each and hold on to them for awhile. usually after years or so of that item not spawning anymore it may be in demand for a decoration.

An example would be the St. Patricks day leprechaun stuff and the easter eggs as well as the jackolanterns. While the jackolanterns are still abundent the lephrechaun suits and easter eggs are considered rare and hard to find. Of course this was many years ago. Still worth it to collect items if you plan to play UO for awhile.

Actually, I'm fixing to shut down my account within the next month.

Then store a bunch of em. If you ever come back, they can help bankroll your restart.

This is why I have like 50 books of truth stashed away lol
I'm also saving a couple complete set of fireworks.. just in case