Originally Posted by Rowan

Another on-the-go solution is to buy some maltrodextrin powder from a home brewing shop. It is a fine white powder that also is called corn starch. It is almost tasteless and can be mixed with water in one of the water bottles so that when he takes a swig he is getting a double benefit of rehydration and refuelling. A few heaped tablespoons full in a 750ml bottle is a starting point.

Maltodextrin/corn starch is a the staple ingedient of the energy bars and drink mixes used a lot by cyclists, including randonneurs, and some are mentioned in this thread. The important part is that it comprises long-chain carbohydrates which even out the energy availability without creating the insulin spkes and mood changes that simple sugars will. Plus it's dirt cheap compared with the commercially produced stuff.