When I was making my winter outfit I had a strip of leftover fleece, which when folded in half looked like a good sized hand bag.
It holds everything I need for a day of temping with fairly consistent weather and temperatures, or everything I need while in transit on a bus going anywhere. The straps are scrap webbing that I diverted from the garbage at a furniture building gig a few years ago. There are loops in all four ends of the straps where I can hook small things, like my keys, phone, and water bottle, for easy retrieval.
The bag measures 43cm x 30cm with a 27cm opening.