Salt pork is meat that has been cured with salt. It is often used as a flavoring agent in dishes such as baked beans.  If you are looking for a substitution, you can use bacon or ham. These options will add flavor to the dish while also providing some protein.  Alternatively, you could use diced onions or green bell peppers to add flavor and texture to the beans. Whichever substitution you choose, be sure to account for the added flavors and textures when adjusting your seasonings.  To attain the desired result, you may need to add extra salt or other spices.