...not so in WA or OR, though I carry a whistle, orange SOS banner, along with a tow strap, hose pinchers (for the clamping off of water line so as to be towed), extra key (they do break or mysteriously disappear) and mini flashlite..
fire extinuisher, if you get right siize one I imagine, does go under the seat, (over the gas tank. and all those fumes

, I'd jump and swim fast and away before trying to remove the seat, get extinuisher and put out MY fire, though it might be handy if you get close to another fire?