I've got bikes in various flavors requiring slightly different kits (and kits for their slightly different uses). All of 'em get a spare tube powdered in a baggie under the saddle and a pump of some sort. They also all get at least a rear blinkie (weight weenies cry all you want, they ain't that heavy). I have tool kits/bags for each of them as well--mostly for my ease of use. The locks and HID front lamps I have one and switch 'em. Too expensive to not do so. If you go the one per bike route then I strongly suggest you standardize what you can. Same CO2 inflators, same multi-tool, same patch kit with 4 quarters and a $20 bill, same half roll of electrical tape, etc.