The food people prepare for
Día de los Muertos is typically (from what I've witnessed) the favorite meals of the of the dearly departed whose spirits are being welcomed back for a visit with family. The food is placed at an altar, or special table which will also include photos of the dead family members/friends, personal effects, etc.
In the way of something "special" and maybe universally or regionally prepared in Mexico for the occasion, other than the
Pan de Muerto and candy which have already been mentioned, I'm not aware of anything.
Regarding
Pan de Muerto, many families have special bread baked for the occasion bearing the family initials or a particular design. The pan can be purchased at Mexican bakeries in the Chicagoland area, and some of the candies also. If you do something special to observe the days make certain to get some marigold flowers, lots of marigolds.
I have about 100 photos uploaded to an online album devoted just to the DoD, including some of DoD altars, maybe a food display or two and lots of photos of the candies.
Mexico: Día de los Muertos
http://travel.webshots.com/album/498584812pZyPVJ