The Seder of Melaveh Malka in accordance to the Kabalists:[1]

After Havdala one is to say Hamotzi over two roles of bread, holding on to only one of them. Prior to the meal he is to recite the Psalm of Mizmor Ledavid Hashem Roiy and then say “This is the meal of David Melech Hamashiach” . He is to then say “Lesheim Yichud.. Hareiny Ba Likayeim Mitzvas Seudas Daled DeMotzeiy Shabbos”.

Drawing the holiness of Shabbos into the weekday:[2]

The purpose of Melaveh Malka is to draw down the holiness of the Shabbos meals into all the meals of the week.

The Luz Bone:[3]

There is a certain bone in the body called the Luz bone which does not benefit or nurture from any food other than the food eaten during Melaveh Malka.[4] This bone is created from the essence of mans seed and cannot be destroyed, not in fire, nor through a grinder, nor through erosion. It lasts forever and is what Hashem will use to build the body by the resurrection. The reason this bone is everlasting is because it did not benefit from the tree of good and evil.

Chibut Hakever:[5]

In merit of eating Melaveh Malka one is spared from needing to experience Chibut Hakever after his passing.

Preventive Medicine for the healthy:[6]

Even if one is very satiated he should push himself to eat this meal, as it will protect his health and save him from needing to eat medicines.

Segula for an easy birth: [7]

It is said in the name of Harav Elimelech Milizensk that it is a Segula for women to have an easy birth if they eat a food in honor of the Mitzvah of Melaveh Malka. They are explicitly to state they are eating the food out of respect for this meal.

Segula to prevent Atzvus:[8]

Eating freshly baked bread on Motzei Shabbos is a Segula to prevent depression.

Segula for Parnasa:[9]

Eating Melaveh Malka is a Segula for Parnasa.

Saves one from heresy and murder:[10]

The Baal Shem Tov stated that in merit of eating Melaveh Malka one is spared from having thoughts of heresy, and is saved from murder

The Neshama Yiseira:[11]

The extra soul which a Jew receives on Shabbos does not leave the body until after the 4th meal of Melaveh Malka. Upon its return the soul is asked “What were you fed? What novelty in Torah did you learn?”. The soul is then elevated to the Heavenly Yeshiva.

Tikkun for the third meal:[12]

The Zohar states: One who does not fulfill the 4th meal of Melaveh Malka is as if he has not fulfilled the 3rd meal either.

The feast of David Malka Mashicha:[13]

The reason that the meal of Melaveh Malka is referred to as the feast of David is because Davis Hamelech was accustomed to make a large feast every Motzei Shabbos out of celebration that he did not pass away that Shabbos, as David Hamelech knew his day of passing would be on Shabbos.

There are also Kabalistic reasons for referring to the meal as the feast of David.[14]

Reciting a story of the Baal Shem Tov:[15]

There is a tradition from Tzadikkim to recite a story of the Baal She, Tov on Motzei Shabbos . The reason for this is because Achiya Hashiloni was the teacher of Eliyahu and of the Baal Shem Tov. Hence just like one is to mention Eliyahu Hanavi he is to mention the Baal Shem Tov.