You can use scraps of fabric or scrapbook paper for the pennants and any string, ribbon, or yarn to hold them together. You will also need either needle and thread or appropriate glue to attach the pennants to the ribbon. After gathering your supplies, draw a triangular template on either cardstock or cardboard to trace onto your paper or fabric. At the top of the triangular template, draw an extra quarter-inch or so (depending on how big your triangle is) to be folded over to create a loop for the ribbon to pass through. You can also glue or sew the pennants directly onto the ribbon, but I think passing the ribbon through loops is a nicer touch. If you are using fabric, I recommend cutting your pennants out with pinking shears to keep them from raveling. After cutting each one, carefully fold the top flap over, and with large (or small, if you want) stitches sew (or glue) it to create a loop for the ribbon to pass through. Once all of your pennants are complete, cut a long enough piece of ribbon, yarn, or string so that you can fit all the pennants on and have enough extra to tie it up where it will hang. Attach either a paperclip or safety pin to one end of the ribbon before you attempt to push it through the loops; this will help you to guide it through them quickly. After pushing the safety pin and attached ribbon through each pennant, hang up your banner and marvel at your handiwork!
Note: If you want the pennant banner to be viewed from two sides, glue two pieces of scrapbook paper together, or sew two pieces of fabric back-to-back. Leave an opening between the two pieces to pass the ribbon, string, or yarn through.