A solid dual-zone cooler keeps your drinks cold and your food frozen on long drives. If you get a quality one, you will only have to buy it once instead of replacing cheap gear every year.
Brands usually drop new models right before the summer rush. If you wait for end-of-summer clearance, you can snag last year's tech for a fraction of the price without losing any real performance.
Remember that the 0% intro APR is a deadline, not free money. If you have a balance left over after 15 months, the bank will start charging interest on whatever you still owe.