DIY fisherman generally do not have a boat and therefore don’t have a boat bag where they can store a bunch of gear. That means your fanny pack needs to carry everything. We have tried a lot of different packs and have settled on the Fish Pond fanny/hip packs with three large sections. When you are walking the flats for eight hours you carry a lot of stuff, all the water required for a day, cameras, lunches, fly boxes, leaders, tippets, clippers, pliers/forceps, sunscreen, glass wipes,etc. Buy a good fanny pack.
At many locations there are limited groceries, no fly fishing shops or hardware stores so think about what you might need. Pack some duct tape (fixes everything) super glue, small tool kit (need screw driver for reels), sewing kit, waterproof bag for your camera, batteries and any food items you can’t live without.