Corporate America begins to assess Sandy's economic impact Two days after the hybrid superstorm tore through the Northeast, businesses from convenience stores to major banks were still making do, relying on generators for electricity and telling employees to continue working from home. For many, staying open has become a balancing act of preparation and improvisation. During the height of Sandy, Mid-Atlantic convenience-store chain Wawa saw about 450 of its 602 stores shuttered - some because of power outages and some that the company closed preemptively. By Wednesday afternoon, only about 80 stores remained closed, mostly because of power outages and because workers couldn't reach some locations in New Jersey's barrier islands. Wawa President Chris Gheysens said in an interview Wednesday that while the company has detailed plans to keep stores open through snowstorms and other harsh weather events, Sandy proved a unique challenge. "What's new here is the breadth of this," Gheysens said of the storm's impact up and down the East Coast. It's a bigger challenge than we've had to face in the past. This is a large-scale effort. That effort meant putting some employees up in hotels so they wouldn't have to commute on dangerous roads and would be nearby when the time came to reopen. It meant keeping critical supply chains open for key products such as milk, eggs, bread and ice, and quickly restocking stores where power had gone out, leaving food to spoil. It meant making sure gas pumps kept running to provide fuel to residents and first responders. It also meant keeping the lights on at stores in any way possible. Gheysens said Wednesday that the company had deployed a dozen generators to Wawa stores where power remained out. "We've cast a wide net looking for more generators," he said. We're just struggling to find them. Gheysens said the company will continue pushing to reopen and restock stores along the coast, in no small part because people in hard-hit communities have few places to go for essential items in the wake of the storm. "They clearly expect us to be there," he said. Many airports in the Northeast were shut down earlier this week, with the storm causing more than 18,000 flights to be grounded. On Wednesday, flights resumed at two of New York's biggest airports, Newark Liberty and JFK International. A FedEx plane was the first to land at Newark when the airport reopened Wednesday morning, said FedEx spokeswoman Shea Leordeanu. The company suspended service on Monday, but all of its planes were operating by Wednesday. Its ground operations were also back up, aside from deliveries and pickups in some areas still deemed unpassable by emergency officials. "We're delivering where it's safe to do so," Leordeanu said. Banks with offices in Lower Manhattan were still recovering Wednesday. Citigroup said its office at 111 Wall St. "experienced severe flooding" and won't be usable for several weeks. The global headquarters for American Express, also in Lower Manhattan, remained closed Wednesday for the third straight day. Spokeswoman Marina Norville said the company was taking its cues from the New York City government, which considers the area an unsafe flood zone. Early estimates from research firm IHS Global Insight suggest that Sandy could cause economic losses of $30 billion to $50 billion. As much as $20 billion could come from infrastructure damage from the massive storm, causing even more widespread flooding damages than last year's storm Irene, which also pummeled parts of the Eastern Seaboard, including New York. The IHS report also noted that Sandy had forced the idling of about 70 percent of East Coast oil refineries, which could drive gasoline prices up in coming days. Some of the losses caused by Sandy likely will be offset by other facts, such as an increase in cleanup and reconstruction activity. But some of the losses - such as spending at restaurants that would have happened had there been no storm - never will be recovered, IHS said.