At the moment getting in to vehicles happens with a single keypress (F) and that causes the character to open the door when necessary, get in to the seat and close the door. I suggest that instead of the single key press you would need to hold the key down during the process. That would lessen the chances of accidental actions and add a simple and easy way to cancel the action when necessary and actually would add a possibility for a new game mechanic without having to add new keys for the new thing.

As an example getting in to a vehicle with doors. Now the one key press opens the door, character climbs in to his seat and closes the door.

I suggest that when you start to hold the key down to get in, the graphic bar that shows your progress in the action (and the animation) is divided in to sections that corresponds to the individual actions that make up the main action, in this case, open door - get in - close door. If you stop holding the button/key down in the first third, nothing changes in the truck, but if you stop in the 2nd third, the character stays out of the truck but the door is now opened and stays open. If you stop holding the button/key down in the last third character gets in to the seat but leaves the door open.