I agree about the mayo thing being iffy -- yes, mayo can spoil, but equivalently, the stuff it is used on can spoil, as well. I think meats (like chicken) are particularly risky. And you are probably better off ordering from a menu (in that the food is more likely to have been freshly prepared just for you). If you do a buffet, go for the earliest seating, while the food is fresh and hot.
I think too that some folks are much more susceptible to food poisoning. My dh and middle child are always the ones to get any stomach flu going around, and always 10 times worse than anyone in our family (usually they end up hospitalized). I have a niece the same way -- yet her sister is not. And I'm not afraid to say I hardly ever ever get these things -- I'm 38 and it just doesn't typically happen to me. DH, in contrast, has landed in the ER at least 4 times and hospitalized twice. DS spent 4 days hospitalized at age 3 for same type thing... like father, like son. But it appears at least the our eldest and dd have thankfully inherited either my resistance or sheer luck -- call it what you will! When we go to Disney, I am the police, kinda "overseeing" who eats what and where! Just wish I could have caught my son before he ate those chicken nuggets at a certain WDW restaurant. It was the only thing different he ate that day from the rest of us, and I'll always wonder that's what caused his gastric undoing later that day. Of course, we eat out maybe once every 2-4 weeks at home; you have to expect higher odds of any illness when you're traveling, if based on nothing more than the sheer VOLUME of opportunities! And typically too you try foods you wouldn't normally, you're drinking different water, you're probably not resting as much as one should; perhaps you even allow yourself to become dehydrated in the Florida sun. All that added together and it's not surprising folks get ill now and then around the 'World.
THis is yet another reason I'm so glad we joined
DVC -- at least some of our meals can be cooked in the villa, where I know exactly how fresh everything is! That has been a big lifesaver (and $$ saver!) for our family of 5, as it cuts us back to eating out every other dinner. Definitely improves our odds for escaping a vacation trip with no stomach upsets!