They've done Bran's entire story from A Storm of Swords
already, so there's not much to do but
get into his three A Dance with Dragons
chapters. Bloodraven is appearing this year, which means they'll be getting through at least two of the three; I expect they'll also do part of the third, which spans a long time and has enough interesting material that it could easily cover the entire fifth season as well.
In the books, Rickon and Osha haven't appeared on page since the end of A Clash of Kings
, but we know they end up on Skagos, an island to the east of the Wall reportedly inhabited by cannibals. Davos is tasked with rescuing them as the price for Wyman Manderly's support of Stannis. What'll happen on the show, I have no idea. There's no information either way on whether Natalia Tena and Art Parkinson did filming for this season.