Just to be clear what 5 de Mayo is....

"The 5th of May is celebrated in the United States among the Mexican-American population, especially in California, Arizona, New Mexico and Texas. Various Mexican-American societies use the celebrations to commemorate the overthrow of the Mexican Imperial Monarchy headed by Maximilian of Austria. The Imperial Monarchy was imposed from 1864 to 1867 on Mexico by Napoleon III, Emperor of France (nephew of Napoleon Bonaparte)".
It was the date on the battle in Puebla Mexico leaded by the General Ignacio Zaragoza, whom won on that encounter. Important, BUT no the most definitive or importance in History as the Mexican Independence in 1810.

This is NOT the most important holiday in Mexico, that would be the Mexican Independence (from Spain) and that is celebrated September 16th.

For entertaining purpose, you could play all kinds of MEXICAN music like, Rancho Grande, Cielito Lindo, in the romantic side, Rhumbas or boleros like: Besame Mucho, Amor, What a difference a day makes(Cuando Vuelva a tu lado), Solamente una vez(You belong to my heart).
If your crowd is younger, any song by Alejandro Fernandez or Luis Miguel....You can YouTube those Mexican artist to get ideas.

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mdorantes