The key in htis is that it's for "personal use" only and the determination is always made by the US customs officer. It's illegal to bring these items back with an intent to distribute, and if you try to come back with 40L of rum of 400 Cuban cigars they're unlikely to believe you.
That said I'd skip cigars entirely (pleh!) and only bring back as much rum as I'd consume in a year or so, assuming it was cheaper in Cuba compared to elsewhere in my travels (i'm rather partial to rum from Belize that's both cheap and really good).