I've long been a user of seat packs for touring, but decided to get something light for road biking - and this hits the sweet spot! No need for a mini-pump as one flat is all you should see, so a 16g CO2 is good. I carry a butyl tube that fits 28-32 mm tires (I use Aerothan, but do not want it for a road-side fix), a Lezyne Trigger Drive and a narrow Topeak Mini 9 Pro (from which I removed the supplied tire levers), plus two normal tire levers. There is room for credit cards, cash, etc.
As someone else mentioned, a Mattone XL that is 15 mm longer and wider would hit the sweet spot for touring and mtn bikes, ie allowing for a bigger tube and a 25mm CO2 cartridge.