Cardenas Market is one of my favorite places to shop in Vegas! Every time I walk in to Cardenas it's like I'm in Mexico at Sorianna or Mega.
Cardenas has one of the best produce departments in Vegas, the meat counter has one of the most extensive selections of meat and poultry around, the bakery is loaded with freshly made Mexican style treats and the cheese/lunch meat counter is awesome.
Two of the coolest things at Cardenas are the Tortilleria and the lunch counter. I don't know of any other place in Vegas where you can watch corn or flour tortillas being made fresh, bagged up and handed to you while they are still warm. The fresh made tortilla chips are the best in town without a doubt. Nearby you will also find a selection of fresh made salsas and guacamole all of which are delicious.
The lunch counter/restaurant is a great place to stop any time of day for some authentic Mexican grub. They have everything from chorizo and egg burritos, asada plates and pork tacos that you can eat while you shop. You may even gain some inspiration for the next Mexican feast you whip up at home.