I used to carry my bike repair kit in one of those wedge bags that fit under your saddle. However, these get wet and muddy in winter and the contents become rusty. Also as an n+1 person (number of bikes required is number you have plus one), I had to try and remember to shift the wedge bag to whatever bike I was riding. The bags are a bit of a faff to undo and re-connect and sometimes I would forget.
So, now I put my complete repair kit inside an old drinks bottle. This contains, spare inner tube, CO2 inflator and bottle of CO2, tyre levers, chain breaker, multi tool, chain quick link. Click on the photo to see what goes in the bottle.
All my bikes have two bottle holders and I hardly ever need to carry two bottles with drinks in them. Switching the tool kit between bikes only takes a moment. I pack the bottle with some paper towel, which stops things rattling and is useful to clean your hand with.