If you have an Aldi where you live, they do their own variety of Quavers, called "Cheese Curls". They are only 3 Syns per bag so would be handy when all of your friends are scoffing crisps. I also like Velvet Crunch or Walkers French Fries (both 4 Syns per bag).
Biscuit / chocolate wise, I would probably take things like: Freddo (5 Syns), Animal bar (5 Syns), Special K Biscuit Moments (5.5 Syns for a pack of 2 biscuits), two-finger KitKat's (5.5 Syns), bags of Fox's Mini Party Rings (6 Syns per bag - alternatively, the normal sized Party Ring are only 1.5 Syns each, but it depends on your willpower not to demolish the whole packet once they're open lol!), Curly Wurly (6 Syns), Daim bar (7 Syns), etc.