You should have received some sort of list of rules to follow as well as what is expected of you during your ER clinical rotation. If you did not receive this information I can give you some help. I have worked as an ER Tech in an inter city level one trauma center for five years the last two have been in the children's emergency department. I do still pull shifts on the adult side and in both positions one of my duties is to work with students during their clinical rotations.
The two most important things to remember are to show up early and be dressed in proper attire. The days of hospitals providing scrubs to students have for most facilities gone away. Check in with the charge RN and find out what is expected of you as well as who you will be following for the shift. You will want to have your stehoscope(around the neck is okay for students) and a pen and something to write on.
This is your time to get as much hands on experience as you can in the time allowed,I see your in for 5 hours,that's not really even near the amount of time you should get. Most EMT-B ER clinical ER rotations are 12-24 hours and that's not enough in my opinion. You may be able to stay for the entire shift which if offered you should jump on it.
Once you have received your tour of the department and and know your limits its time to play. Hint,some of your really sick patients may not come thru the ambulance bays so keep an eye open in triage. Depending on how busy of an ER you have you may spend all your time waiting on an ambulance and miss the really sick one that comes in by POV. If you get a trauma patient be the first in the room with warm blankets in hand. Watch and learn from the team as they do their assessments and put together a treatment plan. Follow the team to the scanner and assist with moving the patient,help with doing a log roll and,watch how they do a back assessment and remove the backboard. Remember to be mature and if you feel you need to leave the room at anytime please do,a sick student is of no use to anyone. What you may be allowed to do is up to the TRN and will differ from hospital to hospital. There wont be much hands on with trauma patients with the possible exception of performing compressions when CPR is in progress. Make sure your up to the task,you don't want to look like a total tool in front of the trauma team. I have seen students who could not do compressions and you don't want to be in that position. Try and get into watch procedures that you may not ever have the chance to see again if you are going to be a field provider.
If the ER has a separate peds section get over there and see what taking care of the little ones is like. This may be your one and only chance to lay hands on some sick kids so take advantage of it,you will be more comfortable working with kids in the field after you have seen the peds ER team work a trauma.
Your time will pass quickly and if you are like I was you wont want to leave so make the most of your time and remember to have fun and learn as much as you can. I have posted replies to other folks asking about student ER rotations,search and you may find a few other things to make your experience in the ER a good one.