How do I get a cam lock out of a really deep hole?
Put some hot glue on the end of a dowel or other stick and put it in the hole.  Give it a minute to dry then gently rotate the stick (and cam) while pulling it out.  Hot glue would be a quick fix, but next step is a stronger glue that might take longer.

Final options - try to drill a hole into the center of the cam lock and threat a small screw into it and pull it out.  Or, if it's not in a very visible spot, drill a small hole in the opposite side and poke out the cam lock with a wire or pin.  Last method is fast, but will leave a visible hole on the "finished" side.