Having done a few bikepacking events this year I have learned a few things that work for me. But what works for me won’t necessarily work for you. Taking in large amounts of carbs just causes heartburn nausea etc ,particularly gels and carb drink mix. Eating little and often is best ,rather than stopping for a big lunch, then facing a long steep climb!
You need to build the resilience to be on the bike for so many hours, which is not do-able on the turbo.(for most of us). Something that worked well for me was to drive to somewhere new ,to make it more fun, then ride out for 10 ish hours, bivvy, or stop in a hotel, then ride back ,a different way to my vehicle. I enjoy route planning so these trips are always fun, and often challenging .
You will learn what kit is best, how to avoid the dreaded saddle sores, and that no waterproof is truly waterproof , and how even your favourite food can make you sick 