I can't imagine why anyone on a cruise would go all the way to
Walmart (which was in Lemon Creek, about half way to the Valley) from downtown just to buy wine. There are PLENTY of liquor stores right downtown (sadly, along with plenty of people who have been at the liquor store--frequently and recently-- hanging out). If you are going to see the glacier, and coming out to the valley, there is a Safeway and a Fred Meyers on the way and both have liquor stores.
That's for Juneau. There are also liquor stores available at the other ports within walking distance of where you'll dock.