I love this idea. An envelope guest book. You just take a store-bought scrapbook/album and glue envelopes into it. Lay out colored pieces of paper for guests to jot notes down on, and then they can place them in the envelopes.
Paper chains Stunning but remarkably easy to re-create. Tissue paper pom poms are easy and fun to make, so are the paper chains! Get friends and family to bake yummy things and tell them its a 'pink theme!