You say camper so I assume elevating food type rather than a coach built Motorcaravan? The reason I ask is because in a Motorcaravan you (usually) have more storage space, possibly a fixed bed, larger kitchen & bathroom areas etc.
The main thing about storage (and weight) is that you should only carry what you need.
Our Motorcaravan is a decent size so storage space isn't an issue but to make sure we make the most of it and to stop the smaller items spreading themselves around is to get storage boxes that fit the spaces.
We put clothes and other lightweight items in the high level storage lockers to keep the COG as low as poss.
Chairs, table, levelling blocks, water container, boots and all "external" equipment etc are all accessed through the external lockers as you don't want to be carrying them through the 'van.
Do you intend having or do have an awning and if so what type (wind out , attached or freestanding)?
Any type of awning is a godsend for increasing usable space but consider if you will be using the 'van when stopping over and how much packing up you are willing to do.
What about power, do you have hook-up, multiple batteries, solar panel etc?
Regardless you want to make sure everything is as energy efficient as poss (i.e. Led lights etc)
Will you be using a TV /radio / DVD player (wouldn't be without ours)? If so, don't forget the ariel lead for plugging in at sites. Also have something to wipe down the hook-up lead when packing it away as they can often be wet & mucky.
Do you have built-in fresh & waste water tanks and if so, are you willing to move the 'van when they need filling / emptying or do you want to leave the 'van in situ?
Of you are willing to move the 'van then no probs (wouldn't work for me though) but I carry a 20L water container that lets me top up the fresh water and a rollalong waste container that allows me to drain the waste a bit at a time.
If away from disposal facilities for some time you may want to consider a second toilet cassette.
The main thing is to get away for as many short stops as you can manage before you use the 'van in anger (several 1-night trips are ideal), if you are missing something you want it to be on a short trip and not a 2-week holiday.
Find out what works for YOU and what items you wished you had packed and see what you thought you may need but then didn't.
The main thing is........ Enjoy it!!!!
Have you joined any clubs (Caravan & Motorhome, Camping etc)? They can give excellent support and access to some lovely sites.
Don't know the size of your 'van but is it covered by your roadside assistance company (over 3.5T, 7M etc are usually excluded from normal car policies)?
What are retail opportunities?