TOD - my first real dress-up affair was my sister's wedding when I was 11 and served as junior bridesmaid (too old to be a flower girl). In addition to the fact that I wore a custom-made dress and dyed-to-match shoes, the day stands out as my first appearance in nylon stockings.
At the University of Michigan, my friend Doug and I decided to attend the gala grand opening night of the Power Center for the Performing Arts, for which I bought a black and white print dress that was slit up both sides almost to the hips and came with a pair of long swishy black pants to wear underneath. The evening was magical with a dedication ceremony, the conferring of honorary degrees on Nancy Hanks, Helen Hayes, James Earl Jones, Walter Kerr, Jo Mielziner, and Julius Rudel and the premiere of the musical THE GRASS HARP.
Now this was the early 1970s and for a subsequent theatre date, Doug dared me to wear the same dress, not with the long pants underneath, but with black "hot pants," which I made myself and had the figure for back then. I think I wore that outfit to Detroit's Fisher Theatre to see PURLIE.
Of course, Richard and I both selected special outfits for our wedding. My veil cost more than my dress, because I bought my dress "off the rack" at a local department store. I really think it was a rejected special order for something like an Eastern Star initiation, but sort of looked like Princess Leia's dress in STAR WARS. Richard drew inspiration for his attire from Lord Peter Wimsey's wedding outfit in Dorothy Sayers' BUSMAN'S HONEYMOON.