Don't be a chump. Employment-at-will means being an asshole is both parties' negotiated default. It says so in your offer letter unless you're at the very highest levels. Now, I have personally extended the courtesy of a multi-month notice to a manager with whom there was genuine mutual respect. But generally speaking, if a company mistreats me the only reason I'll give any notice is because I think it will directly benefit me. For example, maybe it will help to get a better separation agreement.

Is that mercenary? Yes. Do I like it? No, not really. But in the USA where I live it's virtually universal policy with private employers.