The Governor could also hook up with Randal's group if there still around, that would tie that season 2 thread in with Season 4.
Also, the boy 'Toby' (as the Talking Dead calls him) that Carl shot, was he the asthmatic kid earlier in the season they were trying to teach to shoot? If so would is mother then be at the prison now with Carl..hmm.
How are they going to feed that many people in the prison. I guess they really need to fix the outer gates, clear the walkers and garden on the green for starters.