After Thanksgiving, many Hamptons high-flyers headed to a VIP screening of “Saving Mr. Banks,” about the making of the Disney classic “Mary Poppins,” rather than Black Friday sales. Power manager-turned-interior designer Sandy Gallin created an extended dining room at his Amagansett home to host a post-movie meal for 80, where Hugh Jackman led a holiday singalong with Candice Bergen and Bob Balaban. Spotted at the East Hampton screening of the movie — starring Tom Hanks as Walt Disney and Emma Thompson as “Mary Poppins” author P.L. Travers — were Jackman and Deborra-Lee Furness, Lorne Michaels, Itzhak Perlman, Rudy and Judith Giuliani, Donna Karan, diplomat Jean Kennedy Smith (who brought “Dr. Strangelove” editor Anthony Harvey), Christine Schwarzman, Warner honcho Rob Wiesenthal and cartoonist Jules Feiffer. Christie Brinkley rocked up with her kids Alexa Ray Joel, Sailor and Jack, and Martha Stewart arrived directly from Bedford, NY, where she’d hosted a Thanksgiving meal. A spy said many guests were wiping tears away as the PG-13 film ended, and some VIPs then headed to Gallin’s, where he’d transformed an enclosed porch into a dining room for the occasion. Collectible songbooks were on each guest’s plate and Christopher Mason played a shiny black baby grand as guests sang along to “Let’s Go Fly a Kite” and other “Poppins” tunes, spies said.