They sell wine, beer, and liquor at both trading posts. Yes, the prices are high, and it's cheaper to bring your own, but what vacation spot isn't...lol.
Be prepared to pay probably about a 50% markup (depending on your local prices). Trust me, there has been plenty a time when we've run out and decided to make a "golf cart run" to re-stock. Unfortunately in life you have to pay for convenience...lol