Anything you want, but I only put coffee or tea. Sit here all day sipping on a hot beverage.
It insulates. It keeps hot things hot and cold things cold.
A thermos would make a fine gift for a lady tbqh.
Many years ago in my college days I was sitting in Herman Melville lecture when a brunette QT took her seat next to me and produced a fine Nissan Thermos from her backpack. I'll never forget the heavenly aroma that issued forth when she unscrewed the cap and poured jet black steaming hot coffee into the stainless steel cup. It was love.
There is a thermos like this at a peddler's mall near me. Is it worth picking up?