It's actually quite possible to rocket jump in halo reach. of course, it's still not a good idea if you desire to keep your intestines inside your person.
to my knowledge you can't pick up ammo. so you'll run it dry then dispose of it. it's a lot like the m60 in LFD2. super overpowered, but runs out of ammo real fast.
I've been waiting for MvM to be out for some time, and now that it's out i'll be pouring as many hours as i can into tf2. I always did like survival modes, and one in a game as lighthearted and silly as tf2 is a fantastic idea.