One idea for a 50th anniversary party is to purchase a small notebook and have the guests contribute to a list of 50 wonderful things about the couple and their relationship. Another idea is to create a slideshow or collage of photos that commemorates the couple's 50 years of marriage.
Because the 50th anniversary is the "gold" anniversary, the 50th anniversary party can have a gold theme, using gold-colored decorations and tablecloths. Alternatively, the gifts that the guests give to the couple can have a gold theme. The gifts can contain actual gold or incorporate the color gold or the word itself into the gift.