I have been making these flip flops for years, since I played soccer. They are great for teams, fundraisers, gifts, or just for yourself.
You will need a set of flip flops. You can do a plain or patterned like I did.
The thinner the band across the foot the easier this will be. These particualr ones were a little thick.
Then you will need some fabrics. You can mix solids, use one pattern, or several like I did for this post.
I got these, 5 pieces of 18" x 21" pieces from Hobby Lobby for $9.99. Pretty much anywhere that sells fabrics will sell scrap pieces which are great for this, but don't feel bad to go pick some fabrics from a bolt.