What do you ALWAYS bring with you for field work that is not 100% necessary?

I’m a 25-year-old Ph.D. student in Tropical Ecology and Conservation and do/have done my fair share of fieldwork. The more I do, the more I realize there are things I simply do not leave my house without. My number one? portable speaker (with waterproofed power bank). While I love listening to nature’s sounds, sometimes I need a dance party as a to pick me up – It’s a necessity for my mental health.

Does anyone have anything they always bring with them to the field?