My sister and her husband have a couple of Hippy costumes up for grabs to borrow. Go to my still standing blog and lick on The Essex family and take a look....let me know she said she will lend them.
Father and son. You could do a sports theme. Baseball would be good with the backward cap and all. Take two mitts. Play catch. Pick a team and match. You could also do father and daughter. You are so much smaller than him it would be fun.