We bought the Colorations Colorful Collage Kit 5 years ago from Discount School Supply. While it looks expensive, you will use it for years. Every time we run a collage program, I do buy something new to refresh it. This year I added fat yarn pieces in different colors and shiny star stickers.
You will also want some sort of base for your collage. I have used cardstock, paper plates, and various figures. Discount School Supply sells some that are already sticky. Lakeshore Learning sells some where you need glue (unfortunately you won't find them on the web site). This year I found dinosaur shapes at Lakeshore Learning. Each pack of 24 came with 4 different dinosaur shapes.
You will also want glue. Due to the number of people in our program, we pulled out all of our glue sticks and regular white glue. We also got some new glue gel that is awesome. I found ours at Discount School Supply and Office Depot. When back-to-school sales start in the fall, we will be stocking up on this as it doesn't run and it dries clear.
I also pull out our child scissors. With the size of the boards, it is fun to cut the pieces to fit, whether they be feathers, foam stickers, or yarn.
We set up 1 long table at the front of the room for all of the supplies. The kids pick up their collage shape, a paper plate, then pick out what they want to add to it. All of our supplies are on trays or in bins along the table. They take their pile to another table to work on their collage. These tables have the glue and scissors scattered along them. They are also covered in brown craft paper to avoid messes on the tables.
While we say the program is 1 hour, some kids are done in 5 minutes and some take the whole hour. It all depends on the kids and their creations. This is also a great program to stagger registration times if you want to fit in a lot of kids as those who finish in 5 minutes will clear out pretty quickly.