We have been celebrating the beautiful tradition of Dia del los Muertos (Day of the Dead) for years now and I am just now learning about the extended days of it.  
Usually, we put an alter up on, November 2nd, for my in-laws and our previous Boxer, cook the foods they enjoyed (well, not the dog's), share memories, etc.  It's a beautiful way to keep those that have past close.
An AI blurb:
Pagan origins: The celebration originated in a pre-Christian, pagan ceremony by the indigenous Aztec people to honor their dead. It was a month-long festival focused on celebrating the transition to the afterlife, rather than mourning. 
Catholic influence: When the Spanish arrived, they introduced Catholicism. To make their religion more palatable to the indigenous population, they adapted existing rituals. 
Catholic influence: When the Spanish arrived, they introduced Catholicism. To make their religion more palatable to the indigenous population, they adapted existing rituals. 
Syncretism: Over time, the two traditions merged. The pagan celebration was shortened from a month to the two days of observance used in the Catholic church: All Saints' Day (November 1st) and All Souls' Day (November 2nd). Many modern practices, like visiting graves and leaving offerings, have roots in both belief systems. 
Modern holiday: Today, Día de los Muertos is a holiday that mixes these historical pagan and Catholic influences, alongside specific cultural traditions, to celebrate and remember loved ones who have passed away.