I find this the fun part of marketing: creating swag. I recommend making a t-shirt for your movie but it can be anything really, from pens, hats to skateboards. This is for your Folio board so go through sketch and developing process like you would with any other design process.
Once you have several designs you need to mock them up. If you want to see it in real life Redbubble does Print on Demand.
If your drawing skills aren't great then I suggest taking one of the stills from the movie shoot and turn it into a graphic.