There are a few similar threads here -- scroll down the thread list a bit.
Keep in mind that my experiences and practices are based on a long and often painful recovery from injuries and illness. I was diagnosed with Hashimoto's about 20 years ago, a pesky auto-immune disorder that eventually killed my thyroid. There were long periods of time when I could barely get out of bed, let alone exercise. Now, at age 62, I'm cycling at a level just above average for fit men my age. I've even cracked the top ten on a few Strava segments on good days. For me, that's a huge improvement. But what works for me may have little or no effect for folks who are already reasonably fit and performing at a level typical for their age group.
After lots of experimenting with snacks, gels and drinks I've settled on a few that work for me without digestion problems. Some common ingredients in many energy and protein snacks can cause GI upset and gas for some folks. I've had to switch away from sugar alcohols for that reason. While effective for energy with low glycemic index, maltitol made me comically gassy -- like turbo-charged. Not fun for anyone riding behind me.
Most days I mix a quart of an energy/nutrition drink for pre- and post-ride and workouts:
- Cold coffee (whatever's leftover from my morning pot of French press dark roast).
- Six Star vanilla whey powder. I've tried many protein powders, whey and vegan. Legume powders have an awful flavor and texture to me - like dirt. Whey is cheap and it doesn't make sense to overpay. I tried many brands and Six Star is among the best buys with added amino acids and creatine, so I don't need to add creatine.
- Creatine if it's not already in the whey powder.
- L-arginine, if it's not already in the whey powder. Reportedly helps the body produce nitric oxide, especially on sunny days and exposed skin.
- Magnesium lactate -- reduces muscle cramps and burning during heavy efforts such as intervals or climbing.
For much of 2018-'19 I also added several other supplements by cracking open the gel capsules, but that was because I had difficulty swallowing due to a swollen thyroid that distorted and constricted my esophagus and trachea (since resolved with surgery to remove a cancerous calcified tumor). I can swallow capsules again so I no longer add those to the drink.
Bulk Supplements and a few other companies sell common supplements in simple ziplock bags. Often it's cheaper than capsule versions. Those can be added to drinks as well, although some taste pretty bad. The l-arginine, especially the AAKG version I take, tastes a little salty and bitter. But a good vanilla flavored whey powder seems to smooth out the flavor.
I also use niacin, DHEA, pregnenolone, beta-ecdysterone and other supplements. Seems to work for me, especially the ecdysterone (it's derived from greens, including spinach, and from the exoskeletons of some shellfish and insects). But study the available pros and cons carefully before using these. Bodybuilder forums often have more user anecdotes than any other source. I'm not competing in any sanctioned events so I'm not concerned about whether these are considered regulated or banned substances. They're legally available and some experts say there's little or no evidence they actually work. But many users, including me, report good results. (Or we might just be making very expensive urine and enjoying a placebo effect, who knows.)
Often I'll add kratom powder, about 1-2 grams, usually green vein or a blend of green and white vein. This can be controversial. It's legal in most states, but the FDA is considering regulating or banning it. I have chronic pain from having been hit by cars twice with permanent neck damage, shoulder and back injuries. It helps with pain while having few or no detrimental effects. It doesn't make me drowsy or sluggish like my prescription pain meds (which I rarely use, for that reason). There's a slight boost comparable to caffeine. I couldn't have gotten through the past two years of recovery from injuries (and cancer surgery) without it. And I don't say that lightly or without respect for the potential risks that accompany any alternative/herbal products. Study credible literature carefully before deciding whether it's right for you. Avoid the credulous hype from users who claim it's a miracle potion, and ignore the negative hype claiming that it's comparable to opiates. For most of us it's comparable to coffee and NSAIDs for chronic pain, but better. Many folks also report it helps with anxiety. I'd say the pain relief alone is responsible for whatever relief from anxiety I get.
In snacks:
I usually prefer Clif Cool Mint Chocolate protein/energy bars for the flavor, texture and caffeine. If I don't want extra caffeine pretty much any other Clif bar will do. I buy 'em from Kroger because it's cheaper than Amazon and most online retailers.
Ditto, Clif mocha gels for the flavor, texture and caffeine. It's always my go-to gel, after trying many others. I buy 'em by the carton from Amazon since it's cheaper.
Bananas. Lotsa bananas. An athlete's miracle food.