It helps that there's not necessarily a lot to say about some of these 30 DAY CHALLENGE topics. My favorite non-magical item? It's kinda hard to have a favorite. I'll go with the classic longsword. Or, for DEX-based fighters, the rapier as a replacement.
Other than that; these things are so utilitarian that it's difficult to really "like" them; there just there. I don't love my Badger garbage disposal in the kitchen sink, or my claw hammer. I have them, and I need them, and I use them frequently. But it's hard to call that kind of thing my favorite anything.