I was looking at the weekend sale at CSC, and eyeing their "adventure" tank bag. But even on sale at $90, that's just a ludicrous price for a tank bag. So a little shopping later, I found this for $30:
https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1
I put it on last night and it's very nice. Good material, smooth zippers. There is a rain cover in a dedicated pocket. It has a place for a safety harness, but doesn't include it. No matter, I have a bunch of straps and clips and such.
I just wanted something for small things while doing errands on the bike.