Whatever you do, you don’t want to look cheap. Don’t be the person standing there giving out 1 lollipop (like Dum-Dums) or piece of hard candy per kid. And no pretzels. I guarantee they’ll look at each other and roll their eyes as soon as they turn around, if not before. And don’t bother with those cheap "variety packs" at the discout store that contain 15 lbs of candy for $.99. The kids will hate you for life.
I find that M&M’s and Reese’s Peanut Butter cups are popular, and then Kit Kat, Snickers, maybe plain Hershey’s.