Hi Helen, you will have a great time I'm sure, it's a terrific atmosphere up there. I printed my tickets which included Olympic Park tickets and collected my travel passes from the box office there. Don't worry the ticket offices are open, don't bring any booze with you, security take all bottles from you, my bottle of sauvignon was confiscated and I'm sure they enjoyed it lol
There is a variety of food and drink available to buy at fairly reasonable prices, you may even fancy some champagne and oysters there's a whole restaurant available for that very purpose