We've had a thread on what you hauled around northern France and didn't use, but what about things you are really glad you had?
Mine was definitely a very small travel towel (about 15 inch square). My first sleep stop had only paper towels to dry yourself on, and I didn't even bother investigating towel options at the second.
Drying yourself with a 15inch towel is not easy, but I am glad i had it with me!