The service charge is applied to any food and beverage, as well as to any AV services (like if you have an iPod setup at the reception, even if you don't pay a tech to run it). However, while you will be charged tax on the service charge for food and beverage, there is no tax on the AV service charges (that's right - you pay tax on the food/bev itself and then on the service charge for that food/bev

).
There may be other things that get a service fee that I don't know about cuz I didn't use them, but I know that transportation and event guides and Disney photography (or at least the MK photo shoot) don't get service charges.
I love to help out with this stuff because I never would have been able to have a Disney wedding without being able to mock up a budget using info from these boards