I'm not a big fan of jet packs our anything that can make you fly but you need to fly in the end to get around astoroids. I would like to suggest rocket ships that can only be used in the end. Some extra ideas to it would be for some reason you can only craft the ship in parts on there overwold and the parts can only be moved by minecarts . Make them dock to approx astoroids so it's doesn't fly off. Ill leave it here for now it's getting really annoying trying to type this message from my phone. Ill fix the typos tomorrow when I get on a computer