Machaca or Carne Seca can be a great paleo dish, especially prepared from scratch. I would be wary of pre-packaged machaca though as the origin of the (usually) beef is unknown and could contain MSG. You want the ingredients list to say "Beef and salt" or "carne de res y sal yodada" - Nothing more. The Productos del Mayo brand of machaca comes this way, and may be available in your local hispanic market. Better yet, make friends with a mexican grandmother who has probably been making this for decades!