Our local shopping centres often have kids crafty type stuff for free sessions in the school holidays.
We are having a fire and roasting marshmallows tonight, and yes I know you can't do that in other states, but we've used the element on a gas bbq at a pinch before.
lego challenges - I cut up a heap of simple ideas for them to put in a bucket and they pull one out at a time and have a crack
photo challenges/scavenger hunt