If we are physically on it, it we use on.
The boy is on his bike.
The man is on his skis.
They are on the motorcycle.
If we can walk around inside it, we use on.
The kids are on the train.
The pilot is on the plane.
The children are on the bus.
It's fun to be on a ship.
If we can't walk around inside it, we use in.
The man is in his car.
The driver is in his taxi.
The girl is in the van.
Get on Get in
We the bus.
We of the taxi.
We of the car.
We the airplane.
We of a lorry.
We the train.
We of the van.
We the bike.