I have 3 fire extinguishers but, I don't keep one directly by my pit. There of course is one in the kitchen and there are two in my box of competition gear. I don't keep one by the pit mainly because of two reasons. First, I make sure to keep my smokers away from anything flamable, no decks, no wood, no debris, and atleast 15' away from any buildings. Second, other people, if a fire starts in my cooking equipment, I'm going to not just think about putting it out but possibly controlling it and the overall health of the equipment, where as another person is just going to see "FIRE!" freak out and hose down everything without takind the time to realize that they could have done something much different to stop it.
Like I said though, I do keep two with my competition stuff and that's not just because it's a requirement but, you don't know where you might have to set up and the possibility of debris fires due to it and, you don't know who you are cooking next to. They could end up setting your stuff on fire and be more worried about their own stuff than yours.
I do believe it is always good to be safe though, I like to go over "worst case scenarios" with whoever I might have helping me out and how potential problems can be avoided by taking the right precautions.
Better to be safe than sorry.