How long do you intend to ride for with this setup? I ride for 2 hours and use water bottle (in cage, but appreciate not always possible) and bum bag only. This is around FoD, so jacket is either on or left at home.
Bum bag is quite small and was eBay special for about £4 and holds CO2, tube, multitool, tyre levers and still space for battery when nightriding (helmet light with long lead). I found strapping stuff to the bike was less than ideal as it got covered in crap and would come loose eventually.
I’d love a Specialized SWAT box though and then you don’t need to carry anything on you, just bottle in a cage.