Each dress-up day goes with a Dr. Suess book.

Monday - The Cat in the Hat - Wear red & white stripes, silly hats. 
Tuesday - Fox in Socks - Wear your craziest socks!
Wednesday - Oh! The Places You'll Go! - Wear a college or school spirit shirt. School pants required for Mass.
Thursday - I Will Not Get Up Today! - Wear (school-appropriate) pajamas!
Friday - How the Grinch Stole Christmas - Wear a Christmas sweater or Grinch green.