Here is a great idea to correctly flash the pesky “roof to wall” connection. This is were the end of the roof meets the house wall. What happens here if not sealed or flashed properly, water runs down behind the siding or worst in the wall cavity. This picture illustrates by sliding another small piece of siding under the last roof shingle tin, it diverts the water back out to the exterior side of the siding! (The cord is from a Dish network cable)
They ran the J-channel past the end of the roof and kept the angle cut to the bottom of the siding, then slipped a small piece under the siding and shingle tin. Mind you this isn’t the typical 6″ fascia end of the roof, but should work none the less.