How would you respond to someone who says that the big bang is false because explosions don’t produce stuff like matter or energy?

I would say, first of all, that this person is correct in that it is true that explosions do not produce “stuff.”  However, his argument is incorrect for this reason.  The “big bang” was not an explosion.  No one has ever claimed that it was an explosion.  It was a creation.  An explosion turns one form of matter into another with the release of a lot of energy.  That certainly is not what the big bang was.  It was a creation of something from nothing which, by definition, is not an explosion.  The name “big bang” is an unfortunate term.  The beginning of the universe would be more accurately called the big creation event.  The term “big bang” was created by those who strongly opposed the idea back in the 1930s.  They created the label as a derisive term, but, for better or for worse, the terminology stuck.  Your friend is right that explosions do not produce stuff like matter or energy, but the creation event we call the big bang has never been proposed to have been an explosion.

John Oakes