noreen-
I can't imagine that you'll be disappointed with the location of the Westin. Plenty of places to shop for booze and grub, as well as having plenty of local culinary delights at your fingertips! The good news is that places like Pine Peace Mini Mart & Starfish Market both sell pretty much any kind of alcohol that you'd be looking for.
Downtown Cruz Bay is very close. Close enough that I've seen people walking to/from the Westin. I wouldn't do that,personally, with the heat & hills.
Short taxi ride, though.
I'd recommend renting a Jeep. That way you get so much more access to what you want to do, and when. The taxis are great, a little expensive at X amount of dollars(depending on your destination & tipping, which seems to come naturally to most) per person per one way trip. It'll add up pretty quickly. With a Jeep you get more 'bang for your buck'.
Plus, another issue might be that you may potentially waste valuable beach time, as the taxis tend to sometimes stop at most "overlooks" for photo op's. As fun as that can be, I wouldn't want my schedule dictated by a majority of folks that are new to see the island, while you may very well be on your 2nd,3rd,4th(etc...) day trip to or from the beach.
I've taken tours of The Westin, and it's gorgeous! You may choose to not even venture outside of the grounds aside from shopping, but I honestly doubt it.
You'll probably get lots of info & suggestions on this topic, just thought I'd give you my 2 cents.
You're gonna' love it!
Smiles-
MJ

There is a small Deli with some food items + beer & liquor on the Westin Property, and the major, most mainland U.S.-style grocery store on the island, The Starfish Market, is a very short car ride away. Pine Peace Mini Mart & the Dolphin Market are also very close by.