Cake/cup cake decorating, there are 1-3$ bins with kids stuff like pencils and pads and little games or even fun clips for decorating. You can do bows, and goodie bags. There are a lot of great things at Michael's.
Make your own invitations example my daughters birthday theme was strawberry shortcake and with construction paper and glitter I made a strawberry sharp with glitter around it and the leaf to stand out and also got sticky magnets so they can be placed on the refrigerator as a reminder and a favor with a photo of her in a strawberry costume. I also got some clear jars and made candy jars as the favors and tied natural string to look like jam in a jar.