Voltmeter -One of the most valuable tools for boondocking. A multimeter is bunch better but can be tricky for some to use. If your RV has a cigarette plug in it anyone can monitor the volts/state of battery-roughly. If you are charging the battery it will read higher than the battery is and if you are discharging it may read lower than the battery really is.
I would recommend printing something like this out and taping it to a wall by the voltmeter so that anyone can look at it and decide when to use/charge the battery. Most batteries will sustain damage if you take it below 12.2v. Some deep cycle batteries can go down to 10.6 on rare occasions without damage. Very important to check the manufacturer and know your particular battery specifications.
Fire – great for cooking, staying warm and of course telling stories! If you plan on having a fire while boondocking it is imperative that you have some tools to fight the fire. The best tools are a 5 gallon bucket and a shovel. You can always use gray valve and quickly fill a 5 gallon bucket of water, important not to confuse gray and black here! I use the 5 gallon bucket every time I dump the black tank to help ‘flush’ sediments out of tank.
A shovel – has many purpose as well. You can use it to dig cat holes to save room in black tank or shovel dirt on a fire. I have also seen it used to get people unstuck and help level RV’s.
Water – is the most important single item to have. It is a great idea to have an extra gallon or two in jugs so that when your tank runs dry you have a little more. If you boondock by water a water filter may come in handy.
Food – I like to have a little extra when I head out in case I stay longer than I wanted to. Sometimes the weather can dramatically change your plans. Canned food or Mac and cheese are good items to have in the back of the cabinet as they don’t spoil.
Map – Paper is fine but I prefer Maps.me. It is just software for your phone or GPS equipped iPad or electronic device. You will have to download the map areas before loosing cell service. It will show you on a map real time without cell service. Google and Apple Maps are OK, but when your ‘in the middle of nowhere’ Maps.me will show you more detail of trails, mines, springs and other interesting things.