It depends on where you’ll be going. Some of the things in my bag: Rain poncho (very inexpensive, can take up very little room, depending on how thick the material is), energy bars, water, insect repellant, sun block, medical tape, small flashlight, a little bit of cash, etc.
I also have a waterproof container, which contains things like spare cables, lots of batteries (in small plastic cases), extra SD cards (in a plastic case which absorbs some of the impact if you happen to drop them).
You will have to adjust the contents of your bag according to where you’ll be going and how far I’d have to carry said bag. You might have to add some survival items, depending on where you’ll be going.