A printable "Late Pass".
I generally don't use "Free Passes" as I consider any homework or bookwork to be simple practice. While I understand life happens, even for young kiddos, it can't be skipped, but may be late with a pass.
It's nice to have them write out their reason. Sometimes they are funny, sometimes they give you insight into a students home life.
SUGGESTION: I usually print on colored paper. This may help with students re-printing them.