Chex Mix, a few party poppers, a bottle of bubbly: It used to be that anything needed for New Year's Eve could be gotten with a last-minute stop at the corner store. This year, for many folks, it's more than complex. Theyre not simply geting ready for a holiday night, but prepared and provisioned for potential Year 2000 disruptions, shortages, or inconveniences limited at this point only by the individual shopper's world veiw and imagination. One day last week, a fellow bought all of the 15 six-gallon gasoline cans shelved at a Grand Auto store in Santa Rosa. Dried beans, grains, and rice are perenial strong sellers at G&G Market, but typically not in the quantities some shoppers have been lugging off. "You usually don't sell 50-pound bags of barley," said Jodie Lau, an assistant manager.