So after that save file modding thread, I looked up some things on Youtube.
I found this:
It lists all of the vehicles and weapons available in the game. They've went through every possible ID and couldn't find the jetpack or the UFO. They did however mention some DLC vehicles that they couldn't access.
It is pretty sad and hard to admit, but I just don't think that the jetpack and UFO exist in the game as drive able vehicles or equip able weapons, unless they pulled some matrix level sh*t to hide it.