We bought levelling ramps and have used them once in about 10 camping trips. They don’t take up much room. Useful on a sloping site, so you can get the van level. I also bought a small spirit level, though ive also got a app on my phone that does the same thing. Do you need a bike rack? We’ve bought a roof bungee but haven’t used it. Also bought some black carpets, as the grey ones get dirty. We recently bought a ladder for accessing the upstairs bed - not essential but I find it easier to get into the upstairs bed. One of the most useful things we have bought is a small foldable step. It’s only about 12 inches high but very useful for accessing the outside of the elevated roof, especially if you have a thermal topper. I also use it for mounting the bikes on the rack and for cleaning the top of the van. We’ve also bought some Duvalay combined mattress and sleeping bags, which add extra comfort. Also, a Ridge Monkey for doing the cooking.
Still on my “to get” list are some seat covers. I don’t understand why the the standard spec comes light grey carpets and light grey seat trims.