A good set of windshield wipers and a full tank of washer fluid.
It's the kind of thing you don't really appreciate until you're driving through Milwaukee and something is frozen over the little hole where the washer fluid is supposed to come out. I'm a firm believer in "you get what you pay for." Some things (toilet paper, toothpaste, and windshield wipers) are worth spending a little more money on!
What are your splurges?