When you're invited to a BBQ

I am not a vegetarian, but got into an argument after a Facebook post that somewhat called out vegetarians and vegans. My father had thrown a small BBQ and bought, burgers, dogs, chicken kabobs, salads and chips and salsa. Ten minutes before the BBQ he was reminded that one of the kids coming was a vegetarian. So he called her father and asked him to grab something. Problem solved.

My question is, what is your personal protocol when going somewhere and someone might or might not know you don't eat meat? Do you bring your own food to be cooked (which I said was rude) or do you call ahead to remind them of this (which I feel is fine, but a minor inconvenience) or do you just bring something to nibble on?

I should add, 90% of the BBQ i go to have grilled veggies readily available, but this one was small (4 adults 2 kids) and we didn't consider it. Should the responsibility fall on the person throwing the party or the vegetarian?