Smaller Holding Tanks...What to do when NO hookups??

Once had a friend living in a small camper while house was being built. She had a sewer connection as septic was first thing installed but for water, she had to fetch in jerry cans from a neighbor. So she worked hard at minimizing water usage. She managed to get down to 3 gallons a day for drinking, sponge bath, cooking, dish washing and toilet flushing. Clearly that is a bottom limit, but it does suggest that stretching 37 gallons is possible.