Marketplace is open every day. The best times to shop are weekday mornings and afternoons. Bigger crowds often head to Marketplace after Disney World's four theme parks close each day; crowds are also generally bigger on weekends.
Of the 17 stores at Marketplace, a good one to start with is the 50-thousand square foot World of Disney. You can find just about everything on your souvenir list here. Disney Annual Passholders and Disney Visa members can snag extra discounts here, too.
If you have specific items in mind, you may want to meander through Marketplace's smaller stores first. These shops offer merchandise you won't find anywhere else. Find Christmas ornaments, Mickey-themed dinnerware and more.
Don't get overloaded with bags and packages. Disney provides delivery to on-site resorts, and all shoppers have the option of shipping their purchases home for a fee.
You don't want to literally shop 'til you drop. Visit one of Marketplace's fun eateries, like Earl of Sandwich, Rainforest Café or the dinosaur-themed T-REX. Celebrity chef Wolfgang Puck has a fast food joint here, too.