Originally Posted by Cat88L3

You definitely don't need a rental car while staying on the strip. I stayed at the Mirage last year. Planning on Google Maps will be your friend. You will be able to see clearly what's in walking distance or not. There is a Target for sure on the South end of the strip as I walked there from the Cosmo. For water and snacks, I highly recommend going to CVS or Walgreens. They sell liquor there too.
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Anything that isn't walking distance, you can use Lyft/Uber. You also have the public buses for the strip. There are the monorail as well, but I don't find these to be convenient

I'm not sure if the fitness center gives you access to the steam room and hot tubs, but you can quickly solve that by giving the Mirage a call to find out.