How to Include Our Son

My fiance and I have been together for 3 years now and have a 5 month old son, by the time we actually have the wedding he will be 2. I want to find a way to include him in the wedding, not just be the ring bearer, because this is a big day for him, too. His mommy and daddy are becoming one and mommy is going to have the same last name as him. Its going to be a really laid back, back yard bbq wedding with just close family and friends. Any ideas?