Unless I am misunderstanding your post, why can't you file before you go on vacation ? If your green card expires Jan 29th, 2009, you can send in your packet any time after Nov 1st, 2008 (I think that is exactly 90 days before Jan 29th 2009 ??). That way it's all done and you don't have to worry about it after your vacation.
However... you'd still have 27 days to get it in the mail after getting back from vacation anyway. As long as the packet is post marked before the date of your green card expiration you should be good to go. Lots of people (for various reasons) wait until just before expiration of their greencard before filing. I personally had around 30 days of my 90 days left when I sent my packet in.
Edited to add:... You can reschedule your biometrics once you get the appointment. If someone can check your mail while you're away they can find out when the biometrics has been scheduled for. Sending in the packet after you get back should avoid any potential scheduling clashes.
Hope that has helped.
Mark