I suggest either spending it or storing it in the slimefun item called “Flask of Knowledge”
Basically a flask of knowledge is a empty bottle and when u right click it, it will become a xp bottle that you can throw on the floor to gain xp.
I would suggest you to use your xp, on /scroll, enchanting a lot of books or unlocking things in the sf guide. If you used up most of not all of your xp using the 3 methods, you can use the remaining xp to unlock smaller items in the slimefun guide. Slimefun is really fun and is worth a shot to explore the different things you can do with it.
Before going to creative, I suggest using up all your xp using one of the methods above or if your going to wilds, you play at your own risk to lose all your xp.