The term Mardi Gras comes from the French, meaning Fat Tuesday. The holiday gained that designation because people indulged in rich, luxury foods before they began fasting for Lent starting on Ash Wednesday, which usually falls in mid-February - exactly 46 days before Easter. The Mardi Gras season is a time when celebrants ignore normal social convention for boisterous parties, parades with floats, and costumes. The exact date of this carnival festival varies depending on where you live, but it always takes place between Epiphany and Ash Wednesday.
Just Bead It
Create a bead-themed float. One of the most common sights at a Mardi Gras parade is the tossing of souvenirs into the crowd of watchers. Beads are popular with Mardi Gras revelers, as are candies and toy coins. This tradition began in the early 1870s when a masked parade participant on a float, dressed as Santa, tossed little gifts into the crowd. You can use paper mache balloons, painted brightly, for over-sized beads that stream from one end of the float to the other, as if tossed in place. Make larger beads still from beach balls or ball spheres.
Base the theme of your float on the colorful masks people wear as part of Mardi Gras Celebration. In New Orleans alone you'll see everything from clowns and feathers to intricate animal and theatrical masks. That gives you some ideas with which to begin sketching out the masks for your float. Put a large plywood mask in the center of the float and smaller ones all around the sides. They can be dramatic, whimsical, themed to a specific subject matter like the birds or pop culture, or represent your groups fantasies and wishes for the future.
King or Queen for the Day
Construct your float around a central chair that acts as a throne. Adorn the float lushly with purple, green and gold to represent justice, faith, and power, respectively. This idea has a historic origin going back to 1892 when Grand Duke Alexis Romanoff visited New Orleans and asked to be crowned king of the parade. Whoever wears the crown chooses the theme colors for the parade. His choices were purple, green and gold.