Altars or Las Ofrendas or Altares
Las Ofrendas containing offerings of food, drinks and cigarettes to the visiting deceased.
Las Calaveras
Skulls or calaveras are placed on altars. Sometimes a name of a deceased or someone living is placed on the forehead. Some skulls are made of sugar, they are called calaveras de azúcar.
Las Calacas
Statues of skeletons used for Día de Muertos are called calacas. Most of the ones below I bought in Oaxaca City in July 2015 for 45 pesos each or U.S. $3 each. They are about 10 cm (4 inches) in height.

This life sized calaca stood in front of a tatoo shop in Puerto Escondido.

Tapetes de Arena
Sand sculptures or tapestries or in Spanish tapetes de arena are created with sand and pigment, seeds, beans, flower petals and sawdust. These were created at Secondary School No. 86 in Puerto Escondido.
Flowers
Did someone say "marigolds"? Día de Muertos will bring an plethora of marigolds. The smell seems to permeate the town. Marigolds are called cempasúchitl and sometimes caléndula. Their pungent odor helps the deceased find their way home. The purple flower is called celosia or santa teresita, the flower resembles an exposed human brain.
Foods and Candies
Bread of the Dead or pan de muerto or pan de santos is made from egg yolks and is slightly sweetened. They are often placed on altars. They taste great with coffee or hot chocolate.
Art Work of José Guadalupe Posada
Posada used skeletons and skulls, often in costumes, in his drawings and satire. His most well known drawing is La Catrina. Overtime Posada's images of calaveras have become associated with the Mexican holiday of the Día de Muertos. For more on José Guadalupe Posada: José Guadalupe Posada.
Misc.
During Día de los Muertos, copal is used to purify an area and to keep away evil spirits. Copal is a resin from the Copal tree, when burning it smells like pine.
This Day of the Dead couple graced the entrance of the bakery by the market.
