What Bats said! I know of a few classmates that showed up to help 4th years on weekends because they were really interested in seeing something (internal medicine often has busy weekends with admits and procedures) but I never did 😀 You also have no on-call duty.
Pet peeve I had: Clinicians often forget to dismiss underclassmen which sucks. Nothing like sitting around until 8pm only for the clinician to walk into the rounds room and say 'Oh, you guys are still here? You could have left at 4!' What are we going to do, just leave? (some people do exactly that, but you never know when a clinician is going to decide to care about something)
As a 1st/2nd year it really is laid back. You still have to show up, be professional, and participate at the appropriate times, but there isn't a whole lot expected of you. 2nd year is a little harder because you have the milestone/OSCE during your 8th week so you're trying to prep for that. Overall, you're a little bit invisible as an underclassman on the clinic floor but you will be remembered if you stand out in a bad way.
Also don't get frustrated if you're not able to do stuff on real patients. 4th year is the last chance we get to be taught techniques and whatnot so we get dibs! I mostly restrained for my 4th years. You get to see everything though.