We have a trip to London planned in July and I'm wondering whether or not we should take film with us vs buying it there and shipping it back? We'll bring both B&W and color slide film, 100 and 400 ASA, and our flight is non-stop from NYC so we'll pass through xray machines just once (presumably?) in each direction. Carry on vs luggage? Or, if we buy there, where in London would you shop for film?