It varies by location and affluence. When I was going to a public elementary school in the midwest, in the very early 1990s, we had "pizza days" that happened once or twice a month but generally the food was fairly healthy.

I think they maybe had deserts like pudding sometimes. There were no sodas or junk food available at all. The drink choices were 2% milk, chocolate milk, or water.

What I do remember is the food seemed fairly low quality. Canned and frozen packaged stuff, never anything resembling fresh. Every kid got the exact same meal unless you had some medical exemption.

In high school there were some bad choices available in the menu. There were soda and junk food vending machines, but they weren't part of the normal cafeteria and I never had money for them. While there were unhealthy options, there were also many healthy options and you simply bought what you wanted. The freshness was maybe a step up from elementary school.

I think there may have been efforts to remove the vending machines since my time there.