Sadly these change depending on the region you are in.
Some people will say "get in" a ship, or "get on" the queue, but a person from another city or who attended a different school in the same town will say "get on" a ship, "get in" the queue.
I think it is funny when people say "get in a car", because I would say "get into a car" or "out of a car" - getting in a car could mean an item found in a car, or an area big enough to fill with a car.
To an extent you can use what you want. Chances are the verb you choose will be correct for some of the people some of the time, maybe it will make them think you are not from here, but English people listen for regionalisms to give hints if a new person is from another part of the city/country/world all the time.