The first thing to do, IMHO, is to make sure OOO emails are only sent to addresses within your company (at least Outlook has such a setting).
That being the case there is not much to be included, maybe when you'll be back and who to contact if it's urgent but I'm guessing people within your organisation will be able to find who else to contact in any case. The point of the OOO email is then only to let people know that they should not expect a quick reply.
