DS just started kindergarten and I bought him 1 pair of tennis shoes, about 5 pair of pants, 5 shirts and a few shorts.
Last year for pre-k, I bought about the same amount of everything.
I want to add that his birthday is in April and he has lots of shorts/shirts in great condition, as well as another pair of tennis shoes. I also buy him more winter clothes at Christmas.
one suggestion is to check closets and drawers before you go shopping. I didn't realize how many clothes he had. When I wetn to put his new clothes away, I realized that he already has a drawer full of good pants, another full of good shorts, plus one full of good shirts and more nice shirts in the closet. I should've cleaned them all out BEFORE I went shopping, not after. I got rid of lots of nice winter shirts that he barely wore that I bought for school last year, as well as lots of almost brand new sweaters. In florida, long sleeved shirts just really aren't needed. This year, we only bought short sleeved shirts. He has some light jackets/pullovers and a heavy jacket, those are plenty on cooler days.