I spent 8 years 24/7 in a Class C traveling.
Look for multi-use items and figure out WHERE you will store something before buying it. If you can't store it, then it's going to be in the way. Even if you plan to eat out all the time, plan room for some canned and boxed goods. You never know when you may get stuck and hungry.
If you plan to cook a lot, look for collapsible bowls and silicone items, they ride quietly and store easily.
My favorite cookware was chasing down the glass Visionware that works on stove top and in the microwave.
I found that Corelle dishes take up minimal room, ride quietly and are extremely difficult to break or chip, most of mine were bought 2nd hand so that I could end up with a nice assortment of sizes in plates and bowls without having to buy a set that came with stuff I didn't need.
Comfy mugs for hot liquids can also do double duty for cocktails, especially in camps that say no alcohol, pour it in your mug.
For the galley, I also assembled my own nesting pots and pans, colander, etc, they don't seem to sell these as a set, but I was able to put together my own.
Silicone lids in assorted sizes are easy to store and ride quietly, you can toss out the noisy space hogging lids to the pots and pans. They also double duty as covers for other bowls or splatter shield in the microwave.
Figure out your garbage location! I found a space inside the cabinet to hold a round garbage can that can be fitted with the endless supply of plastic shopping bags. I never had to buy garbage bags in 8 years and I hike to the dumpster in the camp daily or more to haul out the trash. If the park recycles, then I use a canvas shopping bag to hold those, then I have two things to carry, one is the recycles bag and other is the little trash bag. I didn't want to dedicate room for massive garbage, and the once or twice daily walk to the dump will do ya good.
Dirty clothes, most rigs don't offer up a space for these. I used a collapsible hamper that I kept in my shower stall. It was easy enough to remove it for showering, then put it back after the shower. I used a microfiber rag (or paper towel) to dry out the shower pan before storing it back in there.
Microfiber towels and cleaning cloths. These dry quickly.
As a female, I also enjoyed a jumbo towel sheet, the kind that you can wrap around your entire body from armpit to knee and tuck in. For public showers or coming out of your own shower, it does dual purpose as a temporary robe.
A big self draining patio mat, I used a 9x12 and learn to fold it properly in 3rds, then accordion style, so it will last years. If possible get one with a bag, easier to store. If you show up and your campsite is all dirt or sand or mud, the patio mat is awesome if you love the outdoors. Also on concrete it works well as then the camp chairs move easily. If you travel with a dog, mine loved the patio mat.
Since I was outdoors a lot, I traveled with a folding card table size, that folded in half again, this makes it easy to store and it was much more comfy to use than the picnic table. Since many camps came with a fire pit grill, I never traveled with a grill.
Don't buy identical outdoor chairs. Get 1-4 assorted different folding chairs if you love the outdoors.
I had a folding rocker, a folding lounge type chair with a high back, a folding directors chair, a collapsible chair that folded up tube length. It was nice to have the different choices of comfort. The zero gravity chairs take up a ton of room when folded up so think twice before buying that style. The collapsible chair that folds up like a long tube with a baggy was handy to lug to the beach in my bicycle basket or to carry over if invited to visit somewhere like an outdoor potluck. Instead of the space hogging zero gravity chair, consider a parachute style hammock. It takes up minuscule room when not in use and it's tons of fun when you are able to hang it up. I didn't travel with a frame, but my friend travels with a hammock frame that comes apart. I just used the adjustable tree straps and some rope. Some camps even came with hammock poles installed on the lot.
Take up bicycle riding, it's tons of fun and quite handy if you have a basket to carry things.
If your Class C has a ladder, then get the metal chair frame rack or 2 that hangs off the back ladder. I have used these to hold all sorts of things, especially when forced to pack up during the rain and stuff is soaking wet. Besides chairs, I've hauled leveling boards tied to them, a step ladder, a vertical bicycle and so on. Also travel with clothes pins and extra plastic coat hangers. You can hang up your towel or any wet clothes pinned to the clothes hanger then hang these off the chair rack hanging on the ladder in back. Triple duty item!
Convert to digital. I copied my CD's etc to MP3 files. I also had digital movies on a portable hard drive so if there was no TV reception and it was raining, I could watch a movie if I didn't feel like reading a book.
Many Class C's don't have shoe storage! In my case, I wear comfy Crocs for everything from hiking to biking to going out. A little soap and water makes them like new again. Try to figure out a multi-purpose shoe you can do everything in so you don't have a shoe storage problem. A compact waterproof windbreaker with hood is a must, takes up minimal room and keeps you dry when it rains.
Tools, I traveled with tools but I was fulltiming. For just camping, you need a small set, but only if you are handy. Things vibrate loose from driving and being able to put them back together is handy. I found that many repairs were from something working it's way loose.
I traveled with a Berkey water purifier, so that no matter where I camped, I had awesome tasting water for drinking and cooing. I never bought pre-packaged water. The Berkey takes up a lot less room than trying to pack away bottled water. Also the filters last years and are renewable with a bit of effort.
Everybody has their own ideas of what to take, these are just some ideas... based on my 8 years of Class C living.
