at the school I was involved with some parents did the following things to help - maybe a list will help to encourage other parents to get involved. Obviously no-one did all these things.
Fete activities for busy people
Take helpers drinks around. This can be done when you have a spare moment so you aren't tied up all afternoon.
Sell raffle tickets/ collect entrance fees if you have them. This has to close before the end of the fete so you spend less time than on one of the stalls
Do "pick a pocket". This is a skirt with pockets and a lucky dip type gift in each. You can wander round with your kids while still making a little money.
Sweets in a jar/ whisky raffle/ guess the name of the toy. Again an activity where you can wander round.
Supplied strawberries at cost price to sell at fete
Made friendship bracelets/ fridge magnets/ scrunchies/ cards/ wreaths at Christmas/ sprayed dried flowers. Some done in groups, some by individuals at home.
Fund raising
Arrange a 70s/80s/90s disco at a local hotel. Get the hotel owner to provide the bar but sell tickets for event.
Quiz nights. I'm the weakest link so not my idea of fun but about 80/100 people used to have a great time with a mix of serious and very silly questions.
Barbecues and picnics. One PTA committee got very hung up about food poisoning then the chair changed No-one has been poisoned and people continue to attend despite appalling weather.
Promises auction. Promises have included anything from a week in a holiday cottage to an hours woodchopping, home meade birthdaycake or free babysitting.
Other things parents have done
Run in the London marathon
Donated end rolls of newsprint to save the school money on drawing paper (check they can use it first).
Donated out grown computer games/ books (again check with head first)/ a clock/ pictures