On my usual 20-30 mile solo training rides I usually don't eat anything. I take water with electrolytes. Usually one bottle in winter, two in summer.
On longer rides, or group rides, I don't like to rely on scrounging whatever I might find along a ride so I take my own drinks and snacks. I stick with whatever I can digest easily and tastes good or inoffensive. Usually Clif mocha gels with caffeine, Clif or Larabar energy bars with a little protein, DripDrop or Propel electrolyte powders. I usually dilute the electrolytes more than recommended.
If I need to eat before a ride I usually stick with the same thing, any time of day or night: oatmeal with one or two eggs (makes a custard consistency, very tasty), a bit of unsweetened Greek yogurt and sliced banana. And coffee.
If I eat or drink anything from a convenience store during a ride it's usually simple sugary stuff like donuts and a canned coffee/energy drink. Monster and others make decent coffee flavored drinks with some protein and supplements that I already take at home anyway. Those don't cause any indigestion.
A few times on long casual group rides we've stopped at restaurants and I tend to eat whatever I like. Then I'm foamy for the rest of the ride. Last time I rode a century I finished the final 25 miles after dinner with friends at a German restaurant. Lots of noodles, pork, sausage, pickled stuff, and 3 or 4 stout German beers. I was burpy and foamy for the last 25 miles. Pizza and beer are even worse, but I still eat and drink the stuff during long casual group rides.
But I avoid that stuff when I'm riding solo or doing the fast club rides. I try to stick with my own snacks and drinks, or simple sugary stuff if we stop after 30-50 miles.
One fellow I occasionally ride with usually takes only a single water bottle on those 50+ mile rides in summer. I don't know how he does it. But he's faster and stronger than I am, and only a few years younger. I think he's 56. Wish I had his energy. I go through both of my 24 oz bottles and need to refill along those same rides, and I go through some snacks. He sometimes doesn't eat anything.