In addition to hot roast beef sandwiches (particularly if you have leftover gravy), cold roast beef sandwiches (slice the cooked meat to get the thinnest possible slices), and cold beef salads, there is roast beef hash.
For roast beef hash, trim and cube or shred beef into barely bite-size pieces. Finely chop a small onion and cube a few cooked medium potatoes, with or without the skin. Put a tablespoon of vegetable oil in a large skillet over high heat. Add all the above when the oil is hot. Fry and turn as the crust forms on the bottom. Season well with salt and pepper and serve when heated through and there is a sufficient accumulation of crusty browned bits.