Have done loads of these for over 10 year so here are some of our most popular:
We have a non uniform day a couple of weeks before and different year groups have to bring in things like chocolate, bottles/tins, smellies, etc.
From that we have a chocolate tombola, general tombola and use the really nice stuff to make up some hampers for a grand raffle (few bottle of wine/nice xmas pud/chocs etc)
Also have a 'pluck a duck' with rolled up raffle ticket stuck in holes on a big wooden shaped 'duck'. Tickets ending in 0 or 5 win and the prizes are cuddly toys dontated in advance (just remembered I've got 3 bin liners full in the loft - must wash them).
Flower pots is always popular - wooden frame with 5 flower pots suspended from strings that hang down the side of the frame. The children pull a string and get the prize under the pot that it lifts up (usually some plastic tat but they love it).
Pick a straw - cut loads of straws in half paint the ends of 1 in 5 and place in tray of sand. Kids pick out the straw and win a prize for getting a painted one (usually a football). Have some cheap sweets/lollies for consolation prizes.
All of the above 50p each or 3 for £1
Lucky dip £1
Santa - definately but do have a number system or some poor kids end up spending the whole fair queueing. If you can get someone to take photos too you can charge about £3 for a visit with present and £5 to include photo.
Craft stall? Might be a bit late now but in the past ours has had a craft group that meet weekly and do stuff for the summer fete and Xmas fair so keep busy all year.
Food - taste of India/China/Carribean, etc (if you have an ethnic mix in the school lots of parents are happy to show off their culinary skills).
Play your cards right - pack of oversized playing cards and a wooden frame. Charge 50p a go and if they get to the end they win £1.
Hook a duck - plastic ducks in a paddling pool. Bamboo canes with curtain hooks -prize for hooking a duck with painted bottom (watch they don't knock the ducks over to check where the winner is )
Splat a rat - drainpipe, stuffed sock,plastic rounders bat - bob's your uncle.
buzzer game
Refreshements (especially home made cakes/fudge/toffee etc)
Get everyone to dress their stalls up with tinsel etc.
TBH the kids just love taking part and winning a load of tat (and yes we are in nice middle class area) and the parents are happy to try and win a nice hamper/bottle of plonk/choccies.
Have a good one