You've reminded me some years ago I donated at a pop up clinic, and it was across the street from a carnival that came to town. They went and got a bunch of ride and games tickets and gave them to blood donors. Big sign over at the carnival, and the clinic was packed.

That's a random way to get people in, but it worked, and it was fun. Now if only they could take the donation while people wait in line for a ride haha.