Try as they might to keep a low profile, it was hard to miss Hollywood hunk Leonardo DiCaprio and his girlfriend, Erin Heatherton , at the Beachside Bistro on Nantucket over the weekend. The cute couple spent most of the day Sunday lounging, eating, and drinking at the seaside spread that’s part of Danielle deBenedictis and Peter Karlson ’s Summer House compound. Hard to say why the pretty pair is here, but Heatherton does have a role in Adam Sandler ’s “Grown Ups 2,” and DiCaprio’s buddy Tobey Maguire is shooting director Jason Reitman ’s “Labor Day” (which was due to shoot in Winchester Monday.) DiCaprio is cooling his heels because the release date of his latest film, Baz Luhrmann ’s “Great Gatsby,” has been pushed to next summer. . . . Boston actress Ari Graynor was at the Revere Hotel on Monday for a screening of her movie “For a Good Time, Call. . . ” She was joined by her costar Lauren Miller , wife of actor Seth Rogen , who has a bit part in the film. . . . Former Celtic Shaquille O’Neal is back in the Bay State to film more scenes for “Grown Ups 2.”