For the record I copy and pasted the below response from another thread but it mostly fits your question as well. Here ya go....
Congrats on your new purchase. I just bought my first RV a few months back and I am still buying things, lol. I just replaced all the lights with LED's from CabinBright.com and I also just installed a new bike hitch rack today. I am well over $1000 in "stuff" for my new to me RV and to be honest I have been frugal with my must have decisions. It all adds up quickly.
Staying over night close by is a must do. Bring a pad and paper and start writing down. But be careful. You will be tempted to buy things that you will never use. Stick to the basic must haves first then move on to your own personal wants.
I did a search for phrases like, "must have RV accessories" and came up with a boat load of things that I consider must haves. That search also brought me here to rv.net where I continue to find more and more valuable info and helpful people.
Here a a few of mine:
1. A rhino sewer hose with an angled back flow extension to clean out my tanks as I don't have a flush valve built in.
2. Decent fresh water hose with a pressure reg where the hose connects to the source. Maybe a filter too.
3. Some kind of storage containers for all of the sewer and water parts and hoses you use. I keep my fresh water lines and black water lines as well as the other things in separate containers.
4. A cheap set of basic tools that stay in the RV if you don't have it parked close to you.
5. A level, Leveling blocks or 2x4's etc... Assuming you don't have hydraulics.
6. Metal tire valve extensions if you don't have them and a high pressure tire gauge and tire covers
7. A folder where you keep all of your records you need to have on the road like insurance, manuals, roadside assistance info and the like.
8. A front door mat. Something hard like astro turf plastic etc...
9. If you have kids or family with you then you must have a stash of games like Uno and more
10. RV toilet paper and RV specific chemicals
11. Toiletries, Bedding, pillows, pots and and, etc...so I don't have to keep bringing from home. Think plastic and cheap for the cups and old pillows and sheets will do.
12. A very small radio. Old school like the Sony ones are great. They run on 2 double AA's.
13. Flashlights, extra batteries, extra power cords for iPad etc...
14. Surge protection
15. A dust buster, broom, mop and basic household cleaning supplies
16. A cast iron pan
17. A small portable heater if you camp in the cold or want to conserve propane.
18. A portable auto battery charger with a high pressure tire inflator built in. I have already used it twice on someone else. Pay it forward.
19. A step ladder. This is a big help for the kids and my wife in our class C
20. THIS IS THE MOST IMPORTANT. Bring a who gives a******what happens, happy ass, adventurous attitude and nothing will ever go "wrong." Leave that grump farter at home. It's time to have some darn fun!!!
I purchased everything on Amazon.com and found them to have the best selection, on hand reviews, and the best price. I don't have a Wal Fart or a Camping World or the like close to me.
Here are a few things you might want to replace/install if you don't already have them:
1. LED lights for dry camping
2. Roof vent covers. Cheap and easy.
GOOD LUCK AND HAVE FUN!!!