Check Your Tires
If you're like most folks, you don't notice your tires until one of them goes flat. But tires are one of the most essential features on a vehicle. First, make sure you don't need new tires by checking for "wear bars" -- darker strips of rubber that show when a tire is hopelessly worn. Even if you don't see the bars, check the tread wear with the time-tested penny trick. Put a penny in the tread and roll it around. If the tread is so worn you can see Lincoln's eyebrow, get a new tire.
Take a look at the spare, too, and know where your jack is while you're at it. If your tires are in good shape, make sure they're inflated to the correct levels -- the right amount of pressure should be listed in your owner's manual. Underinflated tires can explode, which is not the kind of road trip excitement you had in mind.