No need to change the oil for sitting for six months, just make sure it's topped off before you crank it. A change soon thereafter would be smart. If you have the mechanical ability, it's best to turn over the car 15 seconds or more before it cranks to help lube it. You can do that on older cars by disconnecting the coil wire to the distributor, and on electronic ignitions follow the wire to the battery. If you have a pair of jumper cables in your car and you'll likely have a stranger willing to help. Do buy some sta-bil gas treatment, put it in when you fill up according to the directions so that it gets throughout your fuel system. I would recommend having your tank as full as possible to prevent condensation (and to help out any other hikers who make be down on their luck
). Unless you have a slow leak in your tires, they should be fine, just make sure they're properly inflated before you leave. If you're concerned about the finish on your car, wax it before you leave it - if not, make it look dirty and unattractive.
I'd spend another $10 and have a container of brake fluid, power steering fluid and transmission fluid in my trunk to top off if necessary. Generally, you want the car warmed up before you check the transmission fluid level, but if there's something obvious (won't go into reverse, shifts hard) you might want to add some. You may hear some initial knocks and noises from the engine before it picks up the oil, but if they go away after about 5 - 10 seconds you should be good to go.
Take Care,
Tim