We tend to go to the (Perth) Show after lunch (say 1-2pm) and stay til after the fireworks. I explain to the kid what a rip - off show bags are, they can buy double the junk at the shop for half the price! I usually allow $10-15/kid for bags of their choice. 2-3 rides each. I tell them well in advance that they will need to save/earn money for the show and they usually take a bit of their own $. We do all the free exhibits an animals, the kids love them still.
Food - usually take some snacks (apples etc) but generally find plenty of free samples. We buy dinner and eat while watching the arena shows $10/person). I never buy drinks and carry/refill water. Each kid has to carry a backpack - I'm not a packhorse! !