Coworkers, clients, and subscribers typically expect fast responses and solutions to their problems, particularly from people working in customer service, marketing, and communications jobs. Out of office messages provide them with a polite, concise, and professional explanation of why you cannot respond right away. You can provide an OOO message if you are gone for one day, one week, or several months.
I use a basic OOO message – “Hi! I’m out of the office x date(s). I will return your email when I’m back at my computer on x date. If you have an urgent matter, please contact x or y. Have a nice weekend/holiday/etc!/Thanks!” My office WANTS us to use more personal and witty OOO messages like this article’s message. And that stresses me out. I don’t want to spend time worried about whether my OOO is witty. I don’t want to annoy other people just looking for basic info like when am I back and who they can contact in the meantime. I correspond a lot with third parties on serious matters (legal), and I don’t think a message like that is appropriate. So, I just keep using my basic message and hope my supervisor’s supervisor doesn’t email me and see that I’m not “trying.” Ugh.

As to who you choose, you might consider listing a coworker, your supervisor, or an on-call number if available. Just make sure to clear this with whomever you pick as a support person so they’re aware they’re backing up your calls and emails for emergent situations.
I have a confession to make: I haven't recorded a new voicemail greeting in nearly a decade. Since then, I've (hopefully) become more articulate, poised, and self-assured. But hear my voicemail recording, and you'd think I was still new to the work world, a little unsure of myself — and probably not an authority.