Kosher salt is the best option for certain dishes because of its texture, which is coarse and flaky. That coarseness can make the texture of some dishes more interesting. In those dishes, it is usually sprinkled on as a finishing salt.
Some people claim to be able to tell the difference between the flavor of kosher salt and the flavors of other types of salt. This may be because kosher salt is free of additives unlike table salt, which has iodine and anti-caking agents; however, the texture is the main thing that sets kosher salt apart for most people is texture.
In most parts of the US, kosher salt is both affordable and easy to find but there are alternatives if you are somewhere else or have no time to go to the store. Most of the substitutes are just as easy to find and you may have some on your shelf right now.
Your best bet: Coarse sea salt
Like kosher salt, coarse sea salt has large crystals. Its texture makes it the perfect substitute since it provides the same type of crunch, which makes it an effective finishing salt. In addition to that benefit, the flavor of sea salt is almost identical to that of kosher salt. Unlike table salt that is mined from underground salt deposits, sea salt comes from evaporated seawater or water from salt lakes.
In most cases, there is little processing aside from the evaporation. The result is that the trace minerals that are usually removed from table salt can be found in sea salt. Those minerals can affect both the flavor and color of sea salt. Because of the difference in crystal sizes, the amount of sea salt that you use in place of kosher salt is important. Add a single teaspoon of coarse sea salt for every 1 1/4 teaspoon of kosher salt that your recipe requires.
A decent second choice: Pickling salt
If a texture similar to kosher salts is not what you are looking for, pickling salt may be a good option. Like both kosher salt and sea salt, pickling salt does not contain the additives that you find in table salt. In addition, the granules are finer. The smaller granules are what allow this type of salt to dissolve quickly in pickling brine.
If you do not need your salt to provide a crunch or you need rapid dissolution, use pickling salt as your kosher salt replacement. As with the sea salt, you will need to adjust your quantities. Use a teaspoon of pickling salt for every 1 1/14 teaspoon of kosher salt required in your recipe.
In a pinch: Himalayan pink salt
If you are looking for a finishing salt, Himalayan pink salt may be able to provide the cosmetic enhancement that you need. Not only can it enhance your dish in terms of color, but it is also a large grain salt. The large grains allow it to add crunch just like kosher salt. This type of salt has trace amounts of rust in it that give it the characteristic pink color. Along with the iron oxide, it also has trace amounts of important minerals like the other salt types above.
Table salt is easy to find and can provide many of the same flavoring benefits as kosher salt. While the flavor may be an issue for a few supertasters, it is not an issue for most people.
Coarse sea salt is just one type of sea salt; there are fancier versions like Fleur de sel, which comes from Brittany. Fleur de sel is thought to provide a cleaner taste than other sea salts.