I use a Lobo - for everything.
If I need more water than that then a bottle or two on the bike and maybe one in the jersey. Have never needed more than that -even in South of France at midday (if you remember to plan a water stop on your route).
Top pocket for phone/wallet. Bottom pocket for minitools, tubes and keys plus wotnots. Gels in the loops for them. Any extra food in the jersey.
Completed: 94 Stumpjumper w. M733; ; 92 Dave Yates 731 ; 97 Parkpre Pro-Elite ; Pace RC200 F6 ; Pace RC300; 82 Gios Super Record ; 97-8 De Rosa Giro D´Italia; ; Banani SPX Track bike ; 89 Alan/Mavic Cross Bike ; 05 Focus Cross Team ; 90 Look MI-80 all-Mavic ; 12 Focus Izalco Team/custom build ; 11 Focus Thunder Custom build
Projects : , Brouwer all-Mavic
Stripped : Pace RC303
Gone : GT Karakoram
Stayed in the family: Kuota Kharma, 04 Stumpjumper FSR
Ceased to be : Dynatech MT3, killed by corroded seatstays.