As other said, camping toilet. I have a separation toilet, with a bottle in front for the liquids and a box in the back for solids. Bin bag plus wood cat litter in the box, and you're set.
Also a shower tent made from a larger hula hoop and a 180x300 cm shower curtain. I hang it from the tailgate. Doubles as a dressing tent, washing tent and toilet tent (I have a micro camper, or better nano camper - Fiat 500 with seats removed and wooden base plate).
I am using folding boxes in Eurobox size for my stuff, easy to secure in the back, easy to upgrade to a bigger car, easy to put away at home. Want to get wooden lids for them that allow some creativity in using them (Owomo box lids), also for sleeping on top of them. But if you have space enough, the Kallax boxes might be a nicer solution.
Almost everything else I take from my normal household (pots, pans, plates, cutlery, S-hooks, guest airbed, duvet, tarp, laundry dryer for the radiator to hang from the car door, etc. ). If it does the job at home...