Reuben sandwiches consist of rye bread, corned beef, sauerkraut, Swiss cheese, and either thousand island dressing or Russian dressing. The difference in a corned beef sandwich is that it can be whatever you want. Corned beef sandwiches are a combination of corned beef, pickles/pickle relish/coleslaw, cheese, and a condiment sauce like spicy mayo, regular mayo, or mustard.