Yes, it's a real pain to do these things single-handed - if nothing else you'll want to have a run round to see if there are any bargains ( to keep, or just sell on your stall!)
Another handy hint, take plenty of change, fivers etc - punters never have enough change. I've been paying twenties in every shop I've visited for the last week or so!
Don't forget food, water and (if the weather looks good) hat/sunscreen
On-site food is limited to a burger van (often with long queue) and an ice cream van.
Also plenty of bags if you're selling small stuff.
Things tend to start dying out around 1-2PM, or when the weather looks like turning. I usually aim to get there around 9, by which time about half the stallholders have arrived.
Be prepared for vultures to crowd round as you start unloading!