Definitely fairy bread and homebrand cupcakes.
Buy popping corn and do your own (rather than buy the prepacked stuff) - it's cheap as! You can even add food colouring and dye it if you wanted to...
Check out what fruit is selling cheaply and make fruit kebabs. Mini ones on toothpicks are cute for little kids.
If bananas are cheap you can slice, dip in honey and roll in coconut - sooooo delish!
A sausage sizzle if you're having a bbq is cheap. And garlic bread on the bbq is yummo too!
HTH