Originally Posted by Unabomber
The following advice is based on car storage of more than 30 days. While you may use some of this advice for short storage periods, most of it is only applicable for longer term storage.
a. Your battery should be removed. PLAN ON it being dead even if you remove it and place it on a dry, non-conductive surface. Plan ahead and have a charger of some type, another vehicle for jump-starting, or a fresh battery. Your battery WILL be dead no matter what precaution you take and the OEM battery is famous for not returning from the dead, so keep this in mind. Plug in type trickle chargers are another option, but it is generally easier to do one of the above options.
Removing the battery (or just disconnecting it) is a good idea but I can tell you from personal experience that even 2 months is not guaranteed to kill it. We left our 1995 Legacy parked for a month out in the open twice with no special care at all and it fired right up no problem. We also once left a 1990ish Mustang parked for 2 months out in the open with no special care and it also fired up and drove with no problems at all. The only problem we had is once the Legacy's rotors got very rusty and had to be resurfaced (AFAIK the only solution to this is to have someone drive it regularly).