Pizza slices if you have a cooker on site Enormous quantities of cocktail sausages unless you have a significant number of Muslim/Jewish attendees Home made popcorn (and perhaps Nigellas party popcorn for the grown ups)
Big tubs of flapjack bites etc from the supermarket - normally there's some kind of bulk buy offer in the bakery aisle.
I always cut any sandwiches into triangles, 6 per 2 slice sandwich. sound small but tiny sandwiches get eaten much better I find.
plus, dont bring out the biscuits etc until they have had a good stab at the savoury!
choc fingers always a fave. little coloured bowls from somewhere like ikea and put raisins in one, little chip sticks in another, chunks of cheese, pineapple, strawberries, grapes, (halved if any young kids), cucumber chunks etc. looks great on the table.
I save my baking efforts for good slabs of flapjacks and tray bakes for the adults as they are much more appreciative of home baking! the kids just want those luminous party ring biscuits!
Also, it adds to the cost but I tend to provide an assortment of cartons of mini bottles for drinks, put an assortment in piles up the table and let parents help kids select one. It makes for alot less spillage if you are at home.