Wireless- off the top of my head I can't think of a supermarket that you pass on I70 from the airport. I think there is a King Soopers or Safeway just off of the highway around Wheat Ridge (just west of Denver) but I am not sure of the exit. Many of those markets are open late, so I think you should have no trouble finding one open no matter when you are there (some of the King Soopers are 24 hours).
As for markets near Breck, there is a big Safeway in Frisco just off of the highway as was mentioned, and a big City Market in Breck itself just off of Airport Way on your way in to town. These are both big supermarkets that should have anything you are looking for at modest prices compared to small convenience stores (although a bit more than markets down in Denver).