Along the same lines as the toddlers in swimming pools suggestion, how about this one...
"Wash Your Hands!" Especially if you are about to go to the buffet. We all use the same handles, etc. It is far too easy to share germs.
If you use any restroom please wash your hands, or just make a habit of doing it before you go to the buffet. Those gel sanitizers are better than nothing but they don't really do as much as soap and water/ Why? Because whgen you wash your hands it has been shown that most of the germs are left on the towel.
Those gels may not kill ALL the germs and the ones they don't are still on your hands.
So - to avoid spreading disease always wash your hands. And if you are in line in a buffet and have to sneeze - get out of line to do it. people will let you back in.