I was able to scrub in on a surgery last year. I was volunteering in the ER, and a guy came in after dropping a huge piece of metal he was trying to steal on his foot causing a large cut and multiple fractures. The ortho resident came down for the consult etc. I hovered around the bay looking like a lost puppy as I usually do when something interesting shows up. I grabbed supplies for the resident (basin, etc.) and we started talking. He said the guy was going to need surgery for pins/more extensive cleaning and asked if I wanted to watch. I assumed he meant stand in the back and observe, but when I went up to the OR with he and the attending, the attending told me I should scrub in to get a better look. Needless to say I was elated. They used this crazy vacuum thing that I can't remember the name of now to clean the wound, and they actually let me clean it some. I also cut the sutures for the resident as he was sewing up the foot...pretty mundane, I know, but it was awesome to me. It was very interesting and a lot of fun.
There were only 2 nurses, the attending, the resident, myself, and the anesthesiologist in the OR. They were all super nice and explained everything as they went along.