First, I look over the plans for the rest of the classes to make sure I have everything ready and in order. After that, I might work a Soduku puzzle or browse the internet. Each of our schools has a generic login students can use, so I would use that. A lot of sites were restricted (obviously) but I could browse A to Z and a couple of other forums I visit. I didn't log in to post anything, though. Just read over posts I had missed. A couple of times, I was actually asked to cover a different class during the my "planning period", which was fine with me. Sounds like you did just fine. Basically, just letting them know YOU know what they are really doing is all you need to do. That is not just irksome, that is disrespectful and against the rules (in most schools). Students are NOT supposed to leave the room without the teacher's permission, even if that teacher is a sub. I've had some teachers leave a not specifically naming certain students that should NOT be allowed to go to the bathroom. I'm guessing that is a common ruse for those students. Also, I rarely let two students leave the room at the same time, because it's just too easy to lose track of them and I NEVER let two guys or two girls go to the bathroom at the same time. I always tell them they can wait until the first student returns.