Minimal items are always items some often forget when prepairing for a road trip shopping spree. Once you get halfway through the day you will be serioulsy rethinking your choices. Make sure that you wear casual, comfortable clothes that you can move around in when searching for a great deal. I also recommend a small purse clutch for the day that you can carry your money and cell phone in.
Don't forget to put some water bottles in a small travel cooler for the car, bottled water can cost up to $3 at some locations.