I got a nice small (large lunch size) soft sided cooler at Walmart there. We took (cans) beer to the pool as well (we stay at the Marriott Beach Club though).
Definitely Costco is good, and they have poke (I do not care for theirs but I lived on Oahu and am picky), but they also have sashimi which is pretty good. I LOVE Sushi Bay in Kapolei though! OMG we eat there at least every other day when we're there (go early; you have to sign in, it's conveyor belt sushi and SO FREAKING good and cheap, you can also do carry out which we do).
Target also has some liquor but, less selection as Costco, and if you want beer or hard liquor, smaller bottles. If you like vodka, their French vodka is like $20 for a huge bottle!