So she went and got my clothes, put them on, and finished it with a leather jacket and some dark glasses.
I took some photographs of her, doing her best impressions of me being photographed. (This is one.)
Then I drove her to her friend's house.
When she got home, I asked her how it had gone. "Well," she said, "Only one person asked what I was meant to be. I said I was my dad, but they looked sort of blank, so I said I was a secret agent, because of the dark glasses. And they liked that."
Then I made up a tradition of us reading vaguely spooky poems to each other before she went to sleep, Kipling's Smuggler's Song and Monro's "Overheard on a Salt Marsh", the Macbeth "Hubble Bubble" speech and a few more. You can make up traditions if you do it with conviction, and remember to do it next year too.