Here's what I've done: at home I mix up a tub (in an old 5 lb. protein container) of maltodextrin and whey protein in a 7:1 mix by weight. I put 2c. of that stuff in a liter or 24 oz. water bottle. That lasts about 50 miles or between controls or maybe longer. I put however many 1c Ziploc bags are appropriate in my saddle bag to reconstitute as I go. Obviously more bags can be put in a drop bag. That's my between controls nutrition. At a control I get whatever else seems good, mix another bottle and go. I also have a liter bottle of plain water and Endurolytes in a coin purse. I buy the malto in 50# bags from a homebrew supply house or Amazon.
I try to drink a swallow of this mix every 15 minutes, 2 swallows every 30' or whatever. The idea is to drink frequently, so it's a steady drip thing rather than meals. I've described this on BF many times. Other riders have also had success doing this - it's not just nut-case me. I don't get sick of it. The taste is very mild. The issue is that this won't work on PBP unless you have a support person who keeps track of you about every 400k. So there, just put as many croissants as you need into your bar bag. A croissant is about 250 calories.
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