You don't want to spend your barbecue waving at your guests through the kitchen window as you frantically try to prepare dish after dish. Chose dishes that can be prepared in the days leading up to the BBQ and stored easily.
Home made sauces and dips usually keep well for a few days, as do some salads (although if you have a salad dressing, add to the salad on the day of the BBQ). Veggie burgers can be made beforehand and frozen if need be – and if you don't fancy preparing them yourself you can buy in a stock of frozen veggie burgers from the supermarket.
As an example of a tofu burger you can make at home and freeze, try this recipe from every-day-vegetarian-recipes
Don't forget to keep checking Veggie BBQ Ideas for some great ideas for your next vegetrarian barbecue!