When the aliens do arrive you will not be prepared. Even if you have spent half your adolescence and adult life slumped in front of dramatic tales beginning with the word "star" your mind is still going to shut down when escapist fiction becomes hardcore political reality. So you need to prepare NOW. First off you need to take a page from the Mormons and get yourself a year supply of water and food and candles and batteries and stuff. However we really don't know if remaining in our homes is going to be an option so resist any Martha Stewart impulses about prettily arranging canned goods with little labels on them. Pack this stuff into protected sealed containers with the most accessible containers containing your core road trip plan. You will need primarily protein and fresh water, matches, flashlights with long life batteries and a CB radio in your core road trip containers. Your car should have ultra light weight Everest standard sleeping bags in it at all times and an advanced first aid kit. Make sure you know how to use the latter. Though obviously we hope it doesn't come to this you must at all times have road trip plans, maps and an understanding of all potential escape routes. Some may choose to simply leave at the first announcement of alien contact and if you live in a heavily populated urban area you may like to consider this, to avoid a panicked population should leaving become necessary. You can always go back if it turns out to be (highly unlikely) a wonderful development for the planet earth.
Don't forget to replace your water supply with fresh water when needed. Have a list of all your goods, what container they are in and what their use by date is. Have your car's tank full at all times, never arrive home without having topped your tank to the top at the nearest station. Same goes for oil and car maintenance.
The funny thing is, my car currently has a ton of water bottles, granola bars, a sleeping bag, and a tent in it. Not because I'm preparing for aliens, but because I haven't cleaned it out since getting back from Sunday's climbing trip. You've just given me a convenient excuse to leave it a mess indefinitely.