Caffeine has quite a kick the first few times if you're not a regular drinker of coffee, etc. I remember buzzing like a hummingbird the first time I started drinking coffee in the Navy. But after a couple of weeks I barely noticed any effect. It still worked but was more subtle.
That initial buzz could be unpleasant and can provoke a blood sugar drop, but that effect seems to subside with regular use. I remember bonking hard during an uphill group run in military training after drinking way more coffee than usual and a bunch of donuts in addition to eggs and bacon. The sugar buzz was great for a few minutes and then I crashed, hard. Only time that's ever happened. I never tried that combo again before PT.
But the body adapts quickly and I don't notice any buzz. After awhile it becomes more of a necessity just to get moving in the morning. There's also some minor withdrawal symptoms for heavy users -- headaches, etc.
I've cut back a bit on my morning coffee, but all of my usual road snacks and gels have caffeine. My favorites are Clif mocha gel shots, and Cool Mint Chocolate energy bars. Both have about 50 mg caffeine. That's about equivalent to half of my usual mug of coffee. On a hard workout ride I'll use about one gel per hour and it helps. There's a bit more kick than the caffeine free gels and bars.
Occasionally I'll vary snacks but I have no problems with those two Clif products so I usually stick with them. I don't think I've ever had problems with any gels, but have with bars that contain sugar alcohols -- comically ferocious gas. Well, comical for me, not for anyone following me.
I take a bunch of supplements, some unproven, and it's probably just making expensive pee. But if I could keep only one, it'd be caffeine.