Laura, over on I'm an Organizing Junkie, had a great post today about packed activity bags. http://orgjunkie.com/2010/05/storage-star-packed-activity-bags.html
I use a similar system of keeping bags for Tgirl's ballet and bowling, Tboy's soccer or Tball (depending on the season), Tboy's days at Grandma's (she watches him 2 days a week and he goes to preschool 3 days a week), and our summer time pool bag. These all live in the kids' closet. The sports equipment bag (for example the Tball bat bag has his cleats, 3 mitts, balls, bats, and his correct team hat) lives in the back of my minivan. As it is currently off season for soccer, the soccer bag (with ball, soccer cleats, and shin guards) is in the garage.
It is great to know exactly where to put uniform/practice clothes when they come out of the laundry. Then the night before the activity, the bag gets laid out with the clothes, and nothing gets forgotten!
The only downside is when you are so reliant on the system and you do something crazy - like switch cars with your husband. Then you have none of the needed equipment when you arrive at practice. (sadly, speaking from experience)