not much. it's actually pretty easy to protect against cold, vacuum, and heat, even at low levels.

radiation is a lot trickier.

propulsion is the real hard part, unless you bump up the level and allow for either jamming or teleportation. The real problem is that most forms of magical propulsion are fixed speeds, and not acceleration based. With the decanter being the obvious exception, fun choice, btw.

the other real hard part is smacking into something massive at speed... short of walls of force or similar effect, you can't really protect against that much damage.