We usually order wine and beer with snacks and breakfast food from Garden Grocer, but I've also picked up a bottle of wine in the Grab & Go section of the food court. Make sure you have an opener (that was one of my miscellaneous expenses one year).
I've done Mountain Dew for my niece. I bought the small plastic bottles, put them in 2 baggies each (I put them in one, rolled it up, and put them in another) and then wrapped them in my clothing.
We always pack our own booze in our checked luggage. DH will usually buy a small bottle of bourbon - we done both glass bottles and plastic bottles. I just nestle them in the middle of our clothes and have had no problems. I have also packed those small plastic "4-pks" of wine before with no problems.
The grab and go section of the food court as well as the gift shops at the Poly will have six packs of beer and bottles of wine if you don't want to pack it. You are paying Disney Prices for them though.
You could use instacart or another grocery delivery service to have it sent to you as well.