>Vegans should avoid fast food places in general
More like everyone. The only time it's ever acceptable to eat fast food is when you are on a long road trip. If you are on your lunch break, pack a sandwich ahead of time or eat at your workplace cafeteria if your work place has one.

And if vegans want to be consistent with their principles, they wouldn't give any money to businesses that produce and sell animal products at all. Most (if not all) of that money is going to be used to kill more animals.