[mr.spam]

Really depends what they're eating imo. If they're eating chips or similar, I always ask them to put some towel next to them to clean their hands (or to go wash their hands) when they have to touch any cards because I don't want them to get dirty after one evening of play.
Other stuff - like most candy in general - isn't a problem. Bigger stuff - like pizza, kebab, etc. - I always nicely ask them to eat it first, and then continu playing. Never had a problem with it.