All of the above are great suggestions.
Lots of travel size toiletries - body wash, mouth wash etc etc all unscented. A lot of guys may not want to leave smelling of their conquest.. Also opening a fresh bottle of whatever product for that individuals before / after cleanup can help settle the more nervous.
A variety of quality condoms. One size most definitely does not fit all. Also take into account the possibility of latex allergies etc.
Good housekeeping, keep the space clean and tidy. Lots of fresh, clean towels and facecloths. Even though we know better, a lot of guys want to think they are your only client of the day and would rather not see the detritus of previous appointments. Get it out of sight - empty the bins between appointments, get used towels etc out of the way. From experience it can be a little dampening to the mood to see a pile of damp towels in the corner of the bedroom and a bunch of used condoms in the bin.
Febreze is great - a bottle or two of a neutrally scented one, both surface and air freshener can help freshen the room.