Unfinished work
I use a cardboard "mailbox" which most teachers use for papers to be sent home. Every time we transition, if students haven't finished their work, the papers go in their mailbox. Any time during the day they have a free minute, they check their mailbox for unfinished work. If students are absent I put all their work for the day in their mailbox so it's waiting for them when they return. If work has been turned in but needs a lot of corrections (corrections I think the students can do on their own) I also put that back in mailboxes with a note "Please correct this".
This has worked great for me for many many years. It keeps things organized and I can see at a glance who has unfinished work.