I don't ask, but often men bring me my favorite drink (not alcohol lol). Or something they want to see me in-thigh highs a fav for sure! It's not that I'm cheap, but if it is last minute (same day for me). I don't have the time to drive from my job, to the store and make it to the appointment in time. If they ask beforehand, I fulfill most any request within reason.
Otherwise I am prepared-I try to have a variety of condoms, but a couple of clients bring their own (latex allergies etc). That's okay too. @offshore, minty gum or altoids is also something you may want to bring if a provider asks