One of the first things we installed in our popup camper was a collection of waterproof pads for the kids, who were still potty training (as shown by the wet pants hanging in the image above). This post describes some of the specific products we use to keep the mattress and upholstery clean and dry.
One of the easiest and most impactful things for a boondocker to do is replace your standard incandescent light bulbs with an LED version. An LED bulb will use 10% of the energy and last 20 times longer than an incandescent. This means more time between bulb replacement and a lot more time on one battery charge.