Different people have different things that work for them and this is simply what works for us:
1. We carry extra fresh water in refillable 6 gal jerry jugs to put back in the onboard tank
2. I put real tires on our waste water tote do take gray water to the dump station
3. For electrical- use LED lights and turn off everything that you do not need. If you tow with an open truck, you can carry as many batteries in the back as you can afford or have room for. I have two sets of heavy duty jumper cables that I cut the ends off of. One set is hard wired to the onboard battery with a winch connector on the other end. Extra batteries are wired parallel in the back of the truck with the other set of cables attached and another winch connector. When I get to where I am going and unhook, I just hook the winch connectors together. This works for us.