Everyone is different. Our main limitations are water and grey water.
We have 40 USG and find that two adults, showering everyday, use about 5 USG per day.
Our grey tank is just about 10 USG so, unless we are in the boonies, that is the limit. A composting toilet will go two to four weeks.
We have a diesel furnace and good batteries (600Ah) and solar (500w). In the sunny American west we basically cannot use all of the power we generate, even cooking electrically and running the furnace all night. In the rainy east, we have to run the engine during meal prep after about three days. (Actually, we start immediately, but is simply to make it easier on the batteries.)
As with any numbers like these, your results will vary according to your usage patterns, the weather, and your equipment.