I forgot several things, some in the other motorhome, I forgot to move over. The cable link that screws into the motorhome and the site. I finally bought one and the last site had no cable!! The first night the lady at the park loaned us one.
A skillet, had everything else and NO skillet, jeez. Forgot to get the long lighter for the oven, couldn't get the pilot lit with a match, finally got one then decided not to cook in the oven the last night.
The end piece for the sewer hose, took one that didn't fit?? The hose I had wasn't very old and got a hole in it and leaked 3rd night, bought a new set at Walmart and I think someone had taken the piece I needed out of it. But at least its 20 ft long, the other wouldn't have reached at the last place I camped, need to move that adaptor over I have.
Forgot my tire gauge, but not all bad, I got a good long truckers one I really like, keep it tucked under the top step inside, it has a recesed place, keep my gloves in there too.
I think unless you are like some of these fulltimers you will always forget something.