School Battle of Flowers Parade-wear Ideas for 1St Grade Boy

My kids' school is having a Battle of Flowers parade where they will be showcasing (pulling around the campus) floats they have made. I am making a "halo" headband and maybe some jewelry for my daughter who is in 4th grade, but what do I do for my 1st grade SON? They can wear Fiesta or Earth Day styles (the parade will be on April 22nd). They both have bright yellow t-shirts which have been splatter-painted in red, blue, green, and orange. I think that could pass for Fiesta colors. However, what kind of decorations could I make for my boy to wear? I have tons of materials (including undecorated yellow shirts), so I probably have something I can use for almost any ideas y'all throw at me :)

To help the creative juices start flowing: My son's float theme is made on a shoebox. It is an ocean scene with a ship and some water animals on the part painted blue, and land animals and trees on the part painted as grass and sand. These came in a package and are the little wooden pieces with printed pictures that you color and have the little wooden pieces that make the stands.

Thanks for your ideas!