After staying in a Park in a 'full hook up' site that really wasn't (the site had a sewer hookup, but was 40 feet from the rig and I had 30 feet of hose), I bought another length of hose. Used it that one time, stored it away 'just in case' and never needed it again.
Several tools I haven't used, but they are small, and can easily see I could need them.
Lots of spare fuses and bulbs, nuts, bolts, and screws. An assortment in a small plastic vitamin bottle. I have used a few, bit not many.
DW has a few pots and pans she has not ever used. I am smart enough to avoid suggesting she remove them.
An extra box of ammunition. I don't plan on ever getting into a shootout while camping. I cannot envision any worst case scenario where I would need to reload. (DW has used her gun to frighten off a curious and determined bear -- a couple rounds into the dirt next to it. So we'll keep the firearms).
The 'ten essentials' kit in my daypack I use while hiking. But I am not removing them.
About a half dozen different recharger cords for the phones, kindles, etc. Two should be plenty.
Two extra spare inner tubes for the bikes. Only needed one on any trip.
Way more flashlights and hiking water bottles than we need.