They should cut what wasn't necessary at Rivendell, have the dwarves stumble over one fire in Mirkwood, they probably should cut the dwarves' song
, and the lengthy dwarven introduction on Bilbo's porch.
I don't think it would be a good idea to cut Beorn. He's pretty important at the end. He was the one that beat the Goblins basically and saved Thorin.