This has come apropos! I was just teaching my kid (she had an exam of English) from her textbook. In the textbook (of course Indian), there was no comma. If the subject is same, we don't need to repeat the subject. Said that...
Mike went to the shop and brought vegetables -plain and clear.
However, it's good to learn about the Oxford comma if you are including more than two things.
But if at all I want to dig in further, I can think of a context where I'll have to emphasize on the subject because he did something else* than what he was asked!
Say, you send Mike to drop your kid, see a doctor (for some reason), meet a plumber (for some household work), and buy eggs from the shop. Now, he is a forgetful person. He went to the shop but then he bought vegetables. There, I'd emphasize it on the subject by putting it again in the sentence.
And guess what...Mike went to the shop, and he brought vegetables!
I can stress on "...and he...." to prove my point that he actually did go to the shop but he bought vegetables.