My basic bimble kit - I will often add a saw (but that is usually on my belt kit), flint and steel (belt kit again) Trangia triangle (if the weather is foul) or other kit as and when needed.
Here is a set that is basically designed for a quick trip - notebook, pen/pencil, binos, spare glasses, knife, 1st Aid, waterproof/emergency shelter, insect repellent, sweeties, water/brewkit, compass (more for noting nest sites than navigating
) whistle.
Fire/food/brew materials (if I am taking in stuff and not just making nettle or pine-needle tea), leatherman, tissues, Buff etc are either in my jacket and trouser pockets or on my belt.
The bag is made from an old Tipi that was severely rubbish with a rabbitskin cover that is one big pocket. The design is that of a giant Sporran pouch with a drawcord top.