If you're interested in as minimal as possible, I like this one:

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1



It fits what I need: 1 tube, small multi-tool, 2 CO2 cartriges and valve (I use a minimal one), tire levers, emergency butt cream, and nothing else. The way it attaches to the saddle means it doesn't swing like a pair of pendulous bollocks, unlike some bags I've seen.

EDIT: Just to be sure, the one I'm recommending is the "Small" on Amazon's page.