I think this is a great idea! I would include some glamour pictures of actresses of the time; my choices would be Mae West, Fay Wray and Claudette Colbert. Fay Wray would be poignant as her struggle in the arms of King Kong could be reminiscent of Curley's wife's death at the hands of Lennie. The actresses would be in elegant poses, perhaps even with photos of Curley's wife emulating them.
I would include red ostrich feathers as Curley's wife on her shoes, the first time Curley and Lennie see her-
She wore a cotton house dress and red mules, on the insteps of which were little bouquets of red ostrich feathers. (p32)
She may also have a ticket for the Riverside Dance Palace where she met the man who said he would make her a star, and where she also met Curley. She may have pieces of ribbon or fabric which would be fitting for the sort of costumes she would like to wear - red velvet may be a good choice as she shares a love of velvet with Lennie.