Most repair stuff should fit in the seat bag, when it turns warmer ditch the overshoes small waterproof stuck in back pocket with mobile and keys. Pump and water bottle should be on the bike so leaves a bit of space for money and cleat covers if required. As for the ideal bag I use a pe / gym type bag to put anything extra I need to carry into work, like towel and showergel etc as and when required. When it's been emptied at work I just screw it up and stuff it in my pocket.
Posts
retired 9.6kg Carrera Kraken
The Carrera Hardtail combined thread - come on all you Carrera's!
The Sons Scott Genius RC20 build