Don't stop...it is out of way...
I believe you are talking about Cancun. The Walmart is out of your way from airport and you may not get right into your room so if you buy items that need to be kept cold, you will have a problem. I suggest going right to your resort, drop off your stuff. get your room and settle in. The water at the resort will be safe to drink. then when you are ready, take the bus to Walmart. It will cost about 65 cents or 6.5 pesos each. Take abus marked Walmart on window and then ask driver to call out Walmart for you. YOu will be within a block and you just walk down a little street to Walmart. After you shop, you can catch a bus back right at the corner of Walmart to the left as you leave the store. Just look for bus that says hotel zone. If you have a lot of food that might melt or too much to carry, you can get a taxi for maybe $10--12 right at the door. You will be right near La Isla shopping mall at your resort, I believe.
Enjoy.