I am a building sub this year so I am constantly in different rooms throughout the day. I have a pen clipped on the lanyard so I have it handy when I need to write something down, help a student, or help grade papers.
I sneak on some bobby pins too. You never know when a hair emergency will occur!
Behind my badge I keep a whistle. The last thing you want as a sub is to have recess duty and have to call an entire grade to line up WITHOUT a whistle.
It may seem like a lot to have on a lanyard but these are a few things that help make my day go smoother if I have them on me at all times.