PLAN AHEAD! This is your vacation. You've waited a long time to take it, so don't waste any of that precious time shopping for supplies and food. Arrange it all in advance so that you can get the most out of your vacation time.
Entertainment. There will be down time in the evening or even throughout the day, so think about how you'll spend that. Do you like to watch movies? Make sure to download your selections prior to your trip. Like games? Make sure to take a variety with you that you can enjoy either outdoors or indoors, things like cards, board games, badminton, frisbee, etc.
Pack your refrigerator properly. You can't pack the refrigerator completely full. It needs to have air circulation in order to keep the food cold. So you need to take care to pack the right assortment and then refill after a few days. Minimal cold food storage is recommended.
Keep ice in an ice chest with drinks instead of the refrigerator so you always have something cool on-hand. Most RV camping sites have stores where you can replenish your ice supply, or stop in a convenience store in the area.
Know your route. Map it out and make sure you have printouts or paper maps in case you don't have cell service. You don't want to end up on a road that is not suitable for an RV, and no one likes to get lost!
Make your safety checks daily. Service stations are not always close, so you'll want to make sure you are road worthy before taking off to any secluded areas.
Get to your campsite before dark. You want to make sure you've parked in the best location and you'll need to connect all of your hook-ups. This can be challenging if you don't have a clear & well-lit view of your surroundings.
Level your RV Properly. Be sure to level your RV properly - check the packet you were given at the rental site for information. If you don't do this, your refrigerator will not function properly and items may spoil.
KNOW YOUR OVERHEAD CLEARANCE! You don't want to be surprised with getting stuck in a low clearance situation and causing catastrophic and expense damage to your rental.
ALWAYS do a walk around before leaving your campsite: Check that all hoses and electrical are disconnected. Make sure your antenna is down. Secure your awning in the storage position. Make sure all compartments are closed and latched. And confirm that you haven't left anything (or anyone) behind.