I made a jetpack in Minecraft without using mods! To use it, once you have the data pack AND resource pack installed correctly (you can tell which is which because one ends in "datapack", the other in "resourcepack"), inside the game, run the command "function jetpack:equip" and you will be equipped with your jetpack. The jetpack itself does nothing; the jetpack handle is what you need. If you drop the handle mid-air the only chance of survival is to catch it again. You can even drop the jetpack on the ground and it will still work so long as you have the handle. It works KIND of on multiplayer. The only effect it has is when a player using the jetpack starts falling everybody else on the server loses all potion effects. But who actually drinks potions?