I do a walk round, with a check list and check tire pressures, (and state of the tires for checking), fluid levels, (water, oil, fuel), levelers retracted, lockers locked, tags current, steps retracted, wipers in good order, screen wash and leveler fluid topped off.
The whole thing is a walk round from the door, back along the body, round the back, down the other side and return round the front to the door, (I'm not fond of interruptions as I do this, so I try and do it without the kids around to ask me questions, or slow me down, and I follow the same routine after fuel stops for steps, lockers, fluids on the ground, etc).
I will turn on the fridge a couple of days before we set out on a trip, and I leave the interior packing to other members of the family, I do most of the exterior packing, including the camping gear for the kids, mechanical and tool necessities.
The glib answer I was going to give was that before a trip I start the engine, and after a trip I idle it then shut it down!
But I'm grad I didn't give that answer now!