XPBottler is a Paper/Spigot plugin that allows players to put their accumulated experience points into bottles (and vice versa).
To use the plugin, punch an enchanting table with empty glass bottles and they will be filled with the experience the player has. Otherwise, punch them with full experience bottles and the player will regain the empty glass bottles and the experience contained within the experience bottles.
Some logic in this plugin is based on code by Maxopoly.