Congrats on scoring a bib for the marathon! You will crush it!
There's a lot of great advice on here and I'll share a couple things that I think are helpful:
1) I highly recommend the "Fuel for the Sole" podcast and following Featherstone Nutrition on Instagram. Meghann Featherstunn is a registered sports dietitian and a super fast runner. She is so knowledgeable and relatable in the fueling advice she provides through both the podcast and her Instagram account. My family rolls their eyes at how often I say, "well Meghann says..."!
2) There are a couple sites like The Feed and Fuel Goods that let you sample all kinds of different pre- during- and post-fueling options to see what you like and what works best for you. Fuel Goods even has a Featherstone sample pack
As far as where to store all this stuff, I did a combo of my shorts (Lululemon Wunder Train with pockets) and a soft Nathan handheld water bottle when I ran the WDW marathon in 2024. I plan on shifting some of the gels from my shorts to a pocketed running bra I got from Bandit for the 2026 Dopey.