Some of my favorites on my only long backpack were:
Cap'n Crunch with Nido (I wished I had this every day)
Bear Creek Soups with PackIt Gourmet Sour Cream Powder, especially the Chili
Sarah’s chocolate pudding cocoa, I loved that stuff for dessert
When I did the Na Pali Coast, we planned on three nights there. After two nights, we were done. I wasn’t feeling too comfortable with the locals, they barely let you get into camp without telling you all the rules. Then, they are watching you like a hawk, checking on your cooking, water disinfection, and cleaning methods. We brought a bunch of Rice Krispy Treats, homemade beef jerkey, a can of Easy Cheese, a pack of Ritz crackers, a package of pepperoni, a bunch of other regular snack food, and a few dehydrated meals. Everything was eaten but the dehydrated meals. I don’t even think I’d take a stove again. The way there was way harder than the way back. I know it should have been the same, but I guess the diminished food supply helped on the way back. At the time, it was definitely the hardest hike I had ever done. It was also the first time I used hiking poles, and I’ve never gone back to hiking without them. Oh, and try to avoid camping within rockfall distance to the cliffs, we heard them falling all night.
Three weeks? Wow, I hope you have some ideas for things to do there.