I have a buddy who used to do stringer stuff. He made up a card and had it laminated. It said something like "Official Go anywhere vehicle pass. Access all areas. Media" Something like that...
He put it on the dash of his car when he got on scene and said he was never hassled. It looked really official with seals and stamps and whatnot. Total bull but he said even he was surprised the places it got him. Backstage at rock festivals... Fairgrounds...
He had another smaller one made up and put on a lanyard.
That and a lot of chutzpa (sorry, 'schmoozing') can get you a lot of places.
BTW Did you know that DisneyWorld has a policy of free admission to journalists with a valid press pass? You have to contact media relations beforehand and I think you enter through another gate but I am reliably informed that it works. Could save you $50/day on a vacation... Justification? Background research. Especialy now with the Eisner issue...