On longer riders (randonneuring), I've tried putting Perpetuum in my water bottles, and that seems to work okay.
"Energy" drink is ambiguous. Generally, you need calories in a form you can use. You don't need a bunch of caffeine or exotic ingredients.
I quite often buy chocolate milk when I stop at controls, also.
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"be careful this rando stuff is addictive and dan's the 'pusher'."