My PTA volunteer days are a long way behind me but what our school did, from memory (large inner city primary school, over 500 kids on roll):
Disco occasionally in the evening - no idea about this as my children weren't interested
Summer Fair - mostly out in the playground, weather permitting. Involved BBQ with several fathers (yes, I know, very gender stereotyped) grilling burgers and sausages, lots of buns and rolls to hand; Pimms stall; stalls that parents and members of the community could pay to take and sell off anything they liked (probably subject to approval from whoever did the bookings); tombola; etc etc
Christmas Fair - indoors. PTA got permission to use school kitchen (probably tougher to do this now) and sold hot turkey rolls - slice of turkey, stuffing, mayonnaise, cranberry relish, ?salad. Very popular. The turkeys were roasted in various people's homes and brought in to be sliced up. Stuffing probably ditto. Mulled wine stall. Santa's grotto, I think. Tombola. Stalls rented out as above. Raffle.
One issue I remember being raised was when parents who'd rented a stall did something identical to a PTA stall, e.g. tombola. Confusing and possibly the terms of renting a stall got tightened up as a result.
Cake Day. Once a term. Long-standing tradition at this school, but very dependent on goodwill from staff to facilitate it. Now that there's so much more focus on allergies and food intolerances it might be a lot tougher to do this. We had a hut in the playground which was used by the PTA. On the last day before half-term a group of volunteers went in there and set out hundreds of cakes and other baked goods donated by families. Many were from the supermarket but a lot were home-made. Every class in the school came in over the course of the day and each child picked a cake. They had to pay 20p each or something like that (it was a long time ago!). We made sure to have a few things bought in for children with known allergies, so they didn't get left out. I used to help with that and it was good fun.
One of the things we used our funds for was to give each year 6 leaver a book as a leaving present. They picked the book themselves from a list which the volunteer organising this compiled. I did that once or twice and enjoyed it enormously but it was a lot of work, and expensive. Probably an outdated concept now in the days of Kindles, anyway.