Snugglysnerd
I did a car boot sale - going back a few years now though. The things I remember being very surprised at were
Smellies - I used to do Avon so had accrued a bucket load of Avon stuff which I had sampled - so they weren't new - but people couldn't take them off my hands fast enough.
Suitcase - I'd taken clothes over in a few suitcases. People could see the cases and although the baby clothes didn't sell well at all, I could have sold the suitcases umpteen times over!
Clothes for older boys. I took loads of baby boys clothes but they didn't sell at all, and people kept coming and asking me if I had any clothes for older boys. The consensus was that older boys are dead rough and their clothes get tatty fast.
Books - just didn't sell at all. I ended up bringing 90% of them back home and listing them on freecycle just to get rid. The lady who I would say bought 10% was buying for her son who was in the armed forces and she managed to beat me down from 50p per book to 20p and she just took as many as she could carry.
Take lots of change with you - people just don't think, and turn up with notes expecting you to be like a shop! (or maybe they do it on purpose for some reason)?
Also, when you arrive, there are already tonnes of people there wanting to know if y ou're selling any mobile phones, and who try and dive into your bags and boxes before you've set up.
Hope I haven't put you off.