Position racks in the upper and lower thirds of the oven and preheat to 450 degrees F using the convection setting, if available. Place a baking sheet on one of the racks to preheat.
Prepare the chips: Cut the potatoes into 1/4-inch-thick sticks. Toss with the olive oil and cayenne in a bowl. Carefully remove the hot baking sheet from the oven, add the potatoes and spread in an even layer. Use a rubber spatula to scrape any oil from the bowl over the potatoes. Bake on the top oven rack, turning once, until browned and crisp, 25 to 30 minutes. Season with salt.
Meanwhile, make the fish: Set a wire rack on a baking sheet and coat with cooking spray. Lightly crush the cereal in a bowl with your fingers. Add 2 teaspoons salt, and black pepper to taste. In another bowl, whisk the egg whites and a pinch of salt until frothy.
Dip the fish in the egg whites, then roll in the cereal crumbs to coat. Place the fish pieces on the rack (position them on their sides so that the majority of the crust is exposed) and mist with cooking spray.
Bake the fish on the bottom oven rack until crisp and just cooked through, about 12 minutes. Season with salt and black pepper. Serve the fish and chips with tartar sauce and/or malt vinegar, if desired.