I may be wrong, but I understand maltose, being two glucoses linked together, is more evenly absorbed for purposes of strenuous exercise than simple® sugars such as fructose and glucose, and doesn't have as high glycemic response. Maltodextrin is basically a string of glucoses linked together in the same bonding pattern as maltose, (hence the malto-).
Brown rice syrup is made from malted rice, is high in maltose, and is what makes up Clif shots. I use it to make my own cheaper shots, (mix w/ a little choc. syrup, put it in a squeeze tube) though it doesn't taste so good, but where I use it I'm not visiting for gourmet experiences.
Following Twight's advice, I've found staying away from solid foods, proteins, and more than just a bit of fat , sticking to dilute energy drink like Cytomax and maltose/maltodextrin gel shots, works great during the day's exertion at high altitude for sustained energy, is easy on the stomach, though some queasiness is to be expected at altitude. A 16 yo mountain newbie I was with on Adams recently stopped to eat a roast beef sandwich or something, and along with the gatorade (fructose, basically), did a mojo on his stomach that turned him back just a couple hundred feet from the summit. I've seen this wall come up on folk several times, myself included, with those who eat only pop tarts, snacks and whatnot up in the mountains, and get taxed.
The gel shots work, though I am wary of using too many that have caffeine (which seems to in a good number of them). On a few occasions I've given them to a fellow climber/skier when they were waning who hadn't used one before, and they reported a little pickup, though of course this is anecdotal. I think the advice about keeping the energy drink diluted is good as well; A bottle of Cytomax that had been mixed a little strong is what finally set my stomach off at the top of a CO 14er - descent wasn't pretty.