Oh, I forgot about the father/bother merger because it is darn-near universal in the US. My mom is from one of the few places in the US that was non-rhotic and had avoided the caught-cot merger[1], thus resulting in "caught" and "cot" not being homophones, but "cot" and "cart" being homophones.
1: Past-tense because many kids seem to speak much closer to middle-american than even 20 years ago.