I have had my Cali for 9 days now so talking from vast experience:
A porta potti but the smallest, thetford 135. I have one three square inches bigger and the buggeration it causes it might just as well be 3 square metres.
more tea towels than you think you need, brilliant for threading behind the table and eliminating rattles on the move, another one folded between the nesting pans, another one on top of the cutlery drawer...
Carry less food than you think, perhaps enough for a couple of days. I left home equipped to cope with a minor famine and after day one loved walking to the new found chippy, day two the nice pub down the road, day three…. ok, got home and had to junk a lot of unneeded food.
Seat covers are essential, it's amazing what you use that bench seat for, from food prep to propping up a washing bowl.
whichever bed you use, a bed topper. When I hired a vehicle I did not have one and had more aches in more joints than an arthritic centipede. My own vehicle has a bottom bed topper. Never slept better.Amazing difference.
Plastic bags, waitrose, tesco, marks, who cares, the dirty boots/shoes that get put in them aren't fussy. I went very posh and took away exped bags, then got obsessed about getting the bags dirty. Tatty old plastic carriers from the supermarket are brillliant.
patience. It's just soooooooo lovely taking your time because you can do. You can stop when you want, put the kettle on when you want, have a wee when you want, most times find at very short notice somewhere to stop the night when you want. It's the "F" word. I bought my cali for the F word. Freedom.