Every year it’s the same story.All the Conde Nast girls have some item that everyone else wants.A Manolo shoe.A Fendi bag. A Nars nail polish. This year, the situation is a bit more complex. It’s a lunch bag. And it isn’t available at retail.Yes, that infamous cafeteria has yielded a trend: the lunch bag as indispensable tote. As ho-hum as it may sound, all the meticulously groomed PYT’s are toting home their magazines, P.R. graft, and spanking-new Palm Pilots in these pretty blue bags doled out at lunchtime. A bit of intrepid reporting, and we found the source. RTR Packaging, a well-kept secret among the bargain-obsessed (because the upstairs studio sells gift wrap, boxes, bags, and such at dirt-cheap prices), is responsible for this miraculous creation and will custom-make all sorts of wares. But before you get all excited by the 50-cent-per-bag price tag, be forewarned: The minimum run is 3,000. That, sadly, could run you a couple of grand. But, we ask, at what price comes such hipness?