“Ideally, an OOO should include the basics,” says work and wellbeing psychologist Kate Sullivan. “The dates you'll be gone, an approximate timeline for when someone can expect to hear back from you upon your return, and how any urgent requests will be handled in your absence.”
Yes! I hate the “at my earliest convenience” for the same reason – it comes across as “I’ll do it when I feel like it”. I would only use that phrase at work in terms of someone else (ie “at YOUR earliest convenience”).

Get the time and date right for when the automatic emails start - you could choose the the moment that you actually leave the office, or some cheeky people choose an hour or two before they leave, saying that they are busy handing over or wrapping up to deal with customers or other colleagues. They are still able to check the emails they do get anyway, to reply properly to if they want to.
Walk through your office and take a look at your electronics and other potential energy drains. Since you will not be in the office, there is no reason to pay for electricity that you are not using. Make sure that you handle your shutdown properly.