A small mod thats adds a way to store your XP levels
adds a block called Experience Vault, which can store up to 8 experience levels from your XP bar.
Right-clicking the block puts 1 XP level into it, sneaking while right-clicking the block takes 1 XP level out.
Warning: breaking the block while XP is inside will cause this XP to be lost!
(made in a really short time using MCreator)