I'm not sure what you mean by “accidental package”; specifically what kind of accident is involved.
> If it's got your address on it, but someone else's name
Then it isn't addressed to you (the verb address and noun address are related, but not in the use directly corresponding), and isn't what I was talking about.
> If it's got your name and address on it, but the company meant to send it to someone else named dragonwriter instead of you, it's also not your package
This is both generally incorrect and objectively unworkable (it would require an inquiry into the mental state of the sender before one could decide what to do with a package.) There are special cases where things would be different (e.g., there actually is another dragonwriter at the address, who actually did order the merchandise, in which case it is, obviously, not unordered merchandise that they have caused to be delivered to the first dragonwriter. But that's not even an accident or mistake on the sender's part.)
As well as the statute referenced above, the FTC provides clear and explicit guidance: if you receive it, and you didn't order it, it's yours and you may keep it. Intent of the sender is not an issue.
https://www.consumer.ftc.gov/articles/0181-unordered-merchan...
“Q. Am I obligated to return or pay for merchandise I never ordered?
“A. No. If you receive merchandise that you didn’t order, you have a legal right to keep it as a free gift.”
The reason is, the common con game where criminals would send expensive items to someone, often a recently deceased person, and demand payment. The surviving family would assume that good ol' Dad had ordered it and pay up.
The item was usually junk but with a high price tag. So the con had little to lose.
Anyway, items mailed to you without being explicitely ordered are yours to keep, legally.
If it's got your address on it, but someone else's name, it's not your package and you're not entitled to it (in fact, you can't even open it).
If it's got your name and address on it, but the company meant to send it to someone else named dragonwriter instead of you, it's also not your package and you're not entitled to it.
If you order item A and the company accidentally sends you item B instead, that's not "unordered merchandise", that's a mistake, and you're not entitled to treat item B as a gift.