A trick from arctic hunters in the dog sledge era: Get moving about 10 meters (30 feet), then stop and walk all over your camp to look for things forgotten. Of course, it is easier to spot those things dropped UNDER the sledge if you move the sledge first ...

Still good advice, even if the mode of transport has changed.

When leaving home I am most concerned about forgetting my boots or wind&waterproof jacket. It is so easy because you don't nescessarily use them you sit in the car (drive with comfortable shoes, without jacket). Those are two really indespenseable things... I can do without tent pegs (just make 'em from a branch or twig, no problem!) and a lot of other stuff - Hey, improvisation is fun, even if involuntarily! But without my boots or jacket I am really in the cold.... In my climate, the clothes you are wearing are crucial survival items.