You could buy gift cards but i don't see a point as if you were to purchase products/gas there with the credit card you would still earn points. Also, depending on the card, some cards offer additional bonuses when pumping gas.

But the previous posters are right, definitely check out the coin thread as it's the best bang for your buck! =]

You can easily qualify the 5grand spending with no "real" money out of pocket by doing the coins, in less than two months you would meet spending quota!
Good luck