I carry two yes two 750ml bottles. One with one or two tabs of Hi 5 (zero calorie and replacement electrolytes salts etc). If you are a DIY er bit of Orange juice pinch of salt and the rest water. The other bottle is plain water. During the winter months I come back with maybe one of them half full (the plain water usually). During the summer they are always bone dry prior to the end of the ride and my last few miles I am definately dehydrating. My riding is mainly group cycle to somewhere, stop, eat then return home 40-55 miles. Food wise I make sure I have carbs the night before (eg something with wholewheat pasta), I have a breakfast of porridge or oatmeal, scoop of whey protein and maybe some dried fruit (in the porridge) for most rides this is enough to get me to the food stop. I then have something like scrambled eggs on toast and that gets me back home. I do carry an energy bar as well, just in case but Flapjack/cereal bar / fig rolls/jam sandwich - equally serve the purpose. For sub 40-50 miles on a social/easy ride you really don't need to worry too much but longer riding and upping the pace You really do need to eat something that slowly releases energy (complex carbohydrates) and combine that with the bursts of sugar (Gels/jelly babies) to get you through. Each of us is different and it takes a bit of experimentation over a period of time to work it all out.
Very simple to follow is carbs = energy the more complex the carb (porridge) the slower the energy releases the more processed or refined the carb (extreme example jelly baby) short burst of energy, protein = recovery.