In dialogue, is it "Shit," he said, and ran. or "Shit," he said and ran.? (with examples from Heroes and Supernatural)
This question is actually about comma usage in general, not just dialogue specifically.
In any pairing of actions, there shouldn't be a comma if the subject of sentence hasn't changed. (More specifically, there shouldn't be a comma before a coordinating conjunction that does not link independent clauses, but that's a little dizzying.) Since the person/thing doing the actions hasn't changed, the actions themselves shouldn't be separated.
And, so, therefore:
Hiro travels backward in time to save Charlie and falls in love with her instead.
Sam brings donuts when he comes back to the motel, and Dean eats them all by the time Sam gets out of the shower.
Hiro looked at the assembled soldiers. "Shit-u," he said and ran.
Now, if that looks weird, there are a few ways to get around it. You can do this:
"Shit," Dean said, running out of the room as the ceiling began to collapse.
Matt felt the men round the corner a moment before they saw him. "Oh, shit." He grabbed Molly and ran.
With this option, you have to be careful that it's clear who's speaking.
To sum up, if the subject of your sentence (who or what is preforming the action) doesn't change, then you don't need a comma before the coordinating conjunction (and, but, or, etc.).