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.
Replacement is easy. You can pull the old light bulb out and read the exact bulb number, then a quick search on Amazon should provide you with a replacement to all your lights for under $30.
And don’t forget your outside lights. Personally, I haven’t yet changed my tail lamp and running lights, as they run on my car’s power and can’t technically pull from my popup camper battery. But I do have an outdoor light near the door which has been changed to LED.