I also agree with vege sausages/burgers. But as a herbivore myself, I would bring my own alternative, or at least ask the host, they can be more expensive. (My omnivore friends love them too) Roasted vegies - yummy! Thickly sliced red capsicum (peppers??) also go really nicely.
Hi Cheyne, from my POV, it's not the way food is shaped (i.e. hamburger pattie, hot dog, chicken breast) that creates a moral objection in the eyes of vegetarians and vegans, but the fact that it's made out of animal meat. I guess it's easier to make soy and vege protein products shaped like that than say, brocoli shaped.
Also, it's nice to have a "main" part of a meal, along with sides like mash, or vegies. They are also a good way to obtain some of the nutrients vegos need, like iron and protein, because, let face it, most of us love variety in our diet, and eating beans every day isn't much fun! And I do appreciate that with vegetarian sausages and burgers, I could fairly easily integrate into a BBQ like Fidgets without too much hassle, rather than making an entirely different meal.