This is a cool way to pack individual salad servings for picnics or cookouts. You don’t have to use a Mason jar; any wide-mouthed lidded container will do, but the iconic Mason makes for a (somewhat) classier presentation. Blend textures and flavors, use your imagination, consider who you’re feeding, and (above all) make it pretty. If you’re using tomatoes, cut the fruit in half and squeeze out the juices before dicing/slicing for the salad, and I’ll advise against including cheese because it will sweat.
In preparation, sequence is paramount. First in goes your dressing. Make different salads with different dressings for a crowd: a Caesar, a Cobb with blue cheese, an antipasto with vinegar and oil, etc. The next layer should include chunky items: beans, cucumber, carrots, celery, chick peas, green beans, pepper strips, broccoli/cauliflower, sliced radishes, olives, pickled vegetables, and such things. Then diced chicken, sliced eggs, diced (drained) tomatoes, sprouts, diced onions, peas, sliced mushrooms, and nuts. Finally, your leaf vegetables, and this layer should comprise about the top third of the container. Make sure the jars are water-tight before packing in an ice chest.