That little triangle at the front will have some foam in it as well. That's one of the last things I have to do on mine. Asides from adding in some ply to the hull since I messed up and used 1/2 instead of 3/4 - my dad's 180lbs makes the deck bounce. It looks a bit worse when I'm walking on it.
For foam, I used building foam from Lowes. Cost was an issue for me, and my dad had enough for the boat and to finish whatever it was he was doing. Attached mine to the stringers, and left the channel in the middle mostly open.