There are several situations that could strand my kids at school. Our schools won't release the students in any situation unless an authorized individual picks them up and signs them out. I realize that this policy ultimately protects my children. But it also means that my kids could be stuck at school until I can get to them. In some possible emergencies, they could be waiting outside the school in bad weather until I can sign them out.
So, what would I want my kids to have if they were ever in a situation like this? Obviously, I can't expect my kids to carry a huge preparedness kit around with them everywhere. But each child already has a backpack that they usually have with them. Sometimes those backpacks are already pretty full. So in the past, I have filled a small plastic ziplock bag with a few items. Usually there are a few empty side pockets available to stash a little bag.
Here are some things that you could fit into a small ziplock bag:
Family picture (with emergency contact numbers on the back)
If more space is available:
Emergency cell phone
A lot of the schools in our area already have small emergency kits for each student stored in each classroom. It's worth it to become familiar with the safety precautions and preparedness preparations at your children's schools.