I check my tire air pressure on both trailer and suv (or motorhome) the day before.
I fuel up the day before when taking the trailer - like afidel, I'd rather not fuel up with the trailer attached.
Everything gets loaded the day before. I do the trip grocery shopping the day before.
I put a stop on my mail.
I also make sure I have at least one week's worth of meds (for me and Moose-dog) beyond the trip's needs. That allows us the ability to extend our trip. And the meds go in a lock box that helps block odors so Bat-dog doesn't find and eat Moose-dog's pain med.