There is a lot of good advice on this thread. However, I will still give my 2 cents. Save on water and water heater usage; even when the kiddos were small we have boondocked without showering everyday (we have gone as long as three days, utilizing wet wipes (then again I have spent deployments and had no showers for two weeks or more)).
From many of the posts I have read, I think I push the limits on my rig much further than most people do, and tend to do with less.
My DW with two teens and a preteen have gone out for as long as 6 days on 50 gallons of water and no generator, with temps into the lower to mid 20s at night. We utilize a simple 40 watt solar panel to provide a slow trickle charge (which we set up immediately, even in cloudy weather, they will work). We use rigid power discipline. Lights kept off until they are absolutely needed, and turned off when not in use. Utilizing only one light at a time (even with LED's). Using the furnace only during the night with thermostat set around 40. First thing in the morning, I get up and light a burner on the stove to get the coffee brewing, and light the Buddy heater. That warms the TT up just fine until everyone is up and dressed. Water heater is kept off at night and turned on only when the stove is turned off. Again at night just before we shut everything down we run the water heater until it shuts itself off, then turn off the switch so it doesn't ignite during the night. The water stays hot enough through the night that we are good in the morning. We leave the refrigerator running on propane.
Sure the TT gets cold at night, but all of us sleep just fine with an extra blanket or bag.
The reason I mention, holding off on the showers is this; it will save on filling up your grey tank. Plus, realistically, it really won't hurt to skip a day or two.
We wash our dishes in a tub in the sink in the mornings after breakfast. We eat off paper plates and plastic utensils.
In the past we have gone as long as three weeks in our old 5er (which was much older and had incandescent bulbs throughout) on hunts in mid October. We utilized the plugging into the TV every second day for 20 to 30 minutes at idle to charge the battery, and still lasted just fine. We utilized a portable pump platform I built with extension wires off the TV and a hose to refill the FW tank from a mountain stream.
Nowadays I carry a 35 gallon portable tank inside the TT if I am boondocking that long and I have both a 1000W inverter generator and a 5500 watt construction generator if I am out on an extreme cold weather hunt in December where temps drop below zero.
Apologies for rambling. My point is this, you would be surprised how long you can go if you utilize good discipline with power and water usage. Many people get stuck in the mindset where they feel they need to keep their battery (or batteries) completely full everyday, and go into "recharge panic" mode when they see the meter drop to 2/3 charge. I have pushed my down to where it shows 1/3 charge and then drops to E when the heater or stove fan is turned on. Then if I don't have a gen with me, I plug my TV in and let it idle for 20 - 30 minutes.
One final recommendation. I have done this with every vehicle I own and ever TT and camping rig. I load two five gallon gas cans in the back of the vehicle and drive with the TT or under load until I run completely out of gas. This way I know how far I can actually go and then give myself a 30 mile reduction from the total distance so I do not find myself stranded somewhere. I also take the TT out for a weekend (Friday night, Saturday, and Sunday) and disconnect the battery (only connecting it for one hour daily) so we all learn our power discipline and learn how to stay out of the fridge to keep the food cool, etc. it has helped set the family and myself into the mindset.
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