Being served by a waitress:
A woman may not serve a man an alcoholic beverage [i.e. Mezigas Hakos, although she may serve him other foods and beverages]. Some Poskim rule that even other foods may not be served, just like is the law by one whose wife is a Nida. Practically, however, the widespread custom is to be lenient in these matters, due to several reasons: Some are lenient in this as they say the above action of affection is only forbidden to be done by one’s wife who is a Nida, while by another woman it is permitted to do so. Other Poskim rule it is only forbidden to do it in private, while in a public area it is permitted. Other Poskim rule that so long as one is not intending to have these actions done as a form of affection and rather his intent is Lesheim Shamayim, then it is permitted to do so. [Nonetheless, it is proper for one to avoid having a female waitress. If necessary, one should only do so in public, and should try to close his eyes when being served, and she should do so with a Shinuiy, such as with her left hand. It is certainly proper to avoid being served wine and other alcoholic beverages by a woman.]
May a wife or daughter serve food and drinks to male guests?
Yes, as stated above. However, she should not pour wine or other alcoholic beverages for the guests.
Other opinions: Some Poskim rule that the above leniency of the Rashba and Rama ibid is not going on Mezigas Hakos but on other actions, such as eating from the same plate or passing things to each other. [Beis Shmuel 21/9]