I have a Filson Small Field Bag in Otter Green cotton twill, in good used condition - no rips / tears / stains to the cotton, and all the leather is supple and well conditioned. Only 'issue' is that I've lost the shoulder strap (available as spares from Filson).
These are $165 new, so I'm asking $60 shipped worldwide.
From Filson's website:
Ideal for long days in the field, this bag has a large flap completely covering the oval-shaped opening so nothing bounces out....