Barrow of booze raffle
Get parents to donate a bottle of something alcoholic, see if your local off-licence or supermarket will do the same, buy a couple of bottles of spirits or liquers to increase the value of the prize.
Display them all in a wheelbarrow, making sure the pricey stuff is visible, then sell raffle tickets.
In the lead up to Christmas, this can be really popular.
If doing in the summer, include Pimms, fruit cider etc.
Sponsored quiz about the place you live ... we did it as a walk round the village to be able to answer the questions, to be done over half term. Easy version for KS1, slightly harder for KS2, most entries donated £10-£20 and we had a load of gift aid too (registered charity).
I was PTA treasurer for 5 years, despite offering a route for people to just make donations, we only made around £100 a year. Other than the usual Christmas / Summer fairs, the things that made money involved the parents and booze!
DD is at secondary school now, I donate £60 a year to not have to be involved in anything.