I think my stuff would be a combination of the things that others have suggested. I would bring my yellow canvas satchel to carry all of my things. I would bring the following:
A water bottle
A Journal, and surveying tools (@Brendon, you beat me to it on that one. I think it’s a great idea)
A flint and steel
Some smalls snacks, like granola and peanuts
A First Aid kit
A knife, for whatever I would need it for
A light jacket
I’d also walk about with a walking stick as well, probably carved of Rowan.
Edit: I added rope. You can never go wrong with some rope.