I've been working my way through Feed Zone Portables: A Cookbook of On The Go Food for Athletes. The first section reminds me a little of Training for the Uphill Athlete - it feels like a college textbook focused on hydration and digestion. But the bulk of the book focuses on food that supplies energy and electrolytes for endurance efforts in portable packages. A lot of recipes involve making a sheet pan worth of stuff that you can then cut up into bars/etc. It's been a great break from bars and gus etc.