I made myself a little tool kit for gutting catalytic converters.
Tool #1 is a sharpened piece of 3' rebar. That, with a sledge hammer, will break up the cat.
Tool #2 is a modified 1" x 4' box girder. I cut a ½" x 4" slot out of one side. This is used to pull the large/medium chunks out of the exhaust.
Tool #3 is simply a 2" shop vac hose. It is used to collect the dust and medium/small chunks. I often found myself feeding this hose up into the cat, using it to latch on to a chunk too big to go down the hose, and feeding the hose back out and pulling the chunk off the end.