Keep it all. You just don't know what you'll actually use and not use. If you don't need it after all, you can always get rid of it any time. But once its gone, its gone! Besides, those things will not add any extra value to the selling camper.
We purchased 4 campers after giving up tent camping. We kept everything from each change, even everything from our tent camping days. We incorporated them into the new camping module and what we didn't incorporate we eventually gave away. I STILL to this day, have a few items from our pop-up from 1999! We used our tent for years after we got our pop-up, and even then with our first travel trailer. It made a great outside storage area.
Eventually, almost all the extra stuff we ended up not using, after a couple years, were given away. No regrets at all. But there was always the thought, we just "might" want to use this-or-that item. Eventually "this-or-that" was farmed out.