McDonald's will regularly run a 2 for $5 or 2 for $6 Mix And Match deal that lets you pick a couple of fan-favorite items for a low price.  The Mix and Match Menu generally includes the Big Mac, Quarter Pounder with Cheese, Chicken McNuggets, and sometimes the Filet-O-Fish.
Currently, as of October 2022, McDonald's isn't running a Mix And Match Menu special.  However, they've still got plenty of great deals with lots of items for breakfast, lunch and dinner available for $1, $2 or $3!