Original: A well-known accompaniment to steak is shrimp or a cooked lobster tail, a combination often called "surf and turf" or "reef and beef".
Simplified: A well-known side dish to steak is prawns or a cooked lobster tail. This combination is often called surf and turf or reef and beef (the words "surf" and "reef" refer to the seafood and "turf" and "beef" refer to the steak).