The best way to understand what should go in your camper is to move it into your camper, or at least a camper-sized space in your home.
If your build is sufficiently far along, actually put each item in your camper when you decide to keep it. The amount of available space and need for organization will become apparent.
Getting rid of excess material goods takes a long time, and can can be emotionally/psychologically harder than one might think.
Some ideas to help with the downsizing:
“Pack as if you're going out for only a week during the summer. Then add what you'd need if you were going out for only a week in winter. That should pretty much cover everything.” –MrNoodly3)
“I can't be prepared for everything I can possibly imagine, so I prepare for things that are most likely to happen.” – MrNoodly4)
50 ways to leave your clutter:
If you need to jettison books quickly, donate them to your local Friends of the Library group for an upcoming book sale or drop the reading material off at a nearby Little Free Library. – rubbertrampartist5)
Many people have an emotional reaction to physical books are are horrified at the thought of giving them up. But They are bulky, heavy, and we will never read most of the ones we already own. In a van or RV you won't have room to store many of them.
Kindles are popular with 'dwellers they can hold thousands of books in the space of one slim paperback. E-ink models look like real paper and use so little power they can run a month on one charge. Tablet models can do double duty as media viewers, web browsers, etc. Non-Kindle tablets like the iPad or android equivalent can use the free Kindle app.
Your public library probably already digitally loans Kindle books through Overdrive (they are delivered by Amazon). No standing in checkout line or driving back to the library to return them - the books are just deleted from the reader after the loan expires.
If you have books that are not available in digital format companies like 1dollarscan can digitize your physical copy.