The tall Elite one is great. Holds my pump 2xCO2, 80mm valve tube, multi tool and tyre levers plus small first aid kit. You can swap the first aid kit for a small chain lock for cafe stops. The Pro ones are rubbish as the lids fall off. The cheap ones from Decathlon are also good, but shorter so won’t hold my pump. I have several of these.
I run three in total: tall for race and TT bike, small ror fixed wheel (needs a spanner for the wheelnuts) and small for winter bike. The joys of different valve stems. I always havea tube, two CO2 cartridges, instant patches, and a simple tool in each. Pumps live on the fixed bike and winter bike.
Come summer and two waterbottles, I use a pencil case in the back pocket.