People are dressing up again—sort of—as they venture out to social events and prepare to return to the office. Pent-up demand, combined with stimulus checks, rising vaccine rates, new styles and the weight that many people gained or lost during the pandemic, is expected to drive a surge in clothing sales not seen in years, according to industry executives, shoppers and analysts. In the past few weeks, pants with buttons and zippers have begun outselling those with drawstrings or elastic waistbands at L.L. Bean Inc. At Saks Fifth Avenue, sales of dresses, blouses and sandals are exceeding levels not seen since spring 2019. And employees at Haggar Clothing Co.’s distribution center are working overtime to replenish trousers and blazers at department stores and other retailers that sell its clothes. “The fact that sales came back so strongly, so quickly before offices reopened speaks to the need for people to dress up as they get out there and socialize,” said Michael Stitt, Haggar’s chief executive officer.