I'm in a different department than you, which makes a difference, but I will just describe my own experience to give you an idea of what your role may be. Also, I usually only work for four hours a week, so for me it's not time consuming at all.
I work on the oncology nursing floor, which has mostly geriatric patients at my hospital. When I go in, I am assigned to a patient care tech, and I basically act as their assistant. Techs are responsible for the day to day care of the patients staying there, which includes feeding them, bathing them, dressing them, bringing them water/snacks, reporting potential issues to their nurse, doing vitals, and other things like that. This is generally what I do. So far, the only thing that a tech has done that I was not allowed to do was finger sticks for diabetic patients. I'm still allowed to help out with this though, like by using the machine after the tech pricks the patient's finger. That probably doesn't sound too interesting but when you're there it's actually pretty cool. The closest I've got to an actual "procedure" is when I was outside the door of someone getting a PICC Line put in. haha Volunteering has given be a better idea of what it's like to be a nurse or tech than what it is like to be a doctor, but it's interesting and you definitely get patient exposure. You're in the ER though, so it's possible that you may see some more unusual things.
I'm super tired right now so I feel like this has been a really sloppy description. If you want more info just message me, I have a shift tomorrow morning so I'll have more details that will be fresh in my mind. To put it simply, you will definitely get patient exposure but you probably won't see any fancy procedures. For that, you can look into shadowing a physician. Good luck!