I've been doing summer fayres for nursing homes in the area and the mystery bottle stall works really well.
Get loads of bottles of anything (buy cheap ones, ask for donations for something a bit tastier!). It can be wine, whisky, bottled water, vinegar, tomato sauce, anything. I buy bottles now when I see them on BOGOF and then stash them away for the next time. Then get the same number of empty bottles. Fill up the empty bottles with tap water and put the tops back on, stick on a label which says "sorry" or "better luck next time" or "try again". Wrap them all up in newspaper and, mix up the full ones and the mock ones and stand them in crates. Pound a go to pull out a bottle. On the last one I did it was a really hot day and people were just as happy to win a bottle of tap water. I had the water bottles stood by my feet and people were coming along asking if they could buy them!
I've also had a large Connect 4 game which I let kids play for free. While they're amusing themselves the parents talk to us about dog rescue and adopting dogs and volunteering. I borrowed the game from a friend who works for the local youth service, but I've now got a cheap inflatable version myself.
Teddy tombola worked well for us too. Five tickets for a pound, win on a number ending 5 or 0. I got all the teddies from Freecycle. Just get them washed in the machine and hung on the line to dry and they're fine. But make sure you go through the bags and take out the good ones. Sometimes you get quite expensive teddies which make better prizes or special ones (like Christmas themed ones) which would sell in an online rescue auction in the festive season. (Wiccaweys usually have one!)
You also get good books on Freecycle for a book stall. I'm lucky enough to have plenty of storage space at home so I store them in banana boxes (already organised so people can see what's on offer) and just fill up the car with boxes every time I'm off to a show. Pop in a small table, a cover and a poster with prices on and you can set up in 5 minutes flat. Any that don't sell come home with me for the next time.
Good luck!