I used to get terrible blisters on the bottom of my heels. I have found that wearing moisture wicking socks and applying body glide works for me. If I get any blisters on my heels I just put a blister bandaid on and I'm good to go.
I had this happen a few years ago in Las Vegas, doing alot of walking. I would recommend 2 things:
the cushions Dr.Scholls makes that fit in your shoes-and a comfortable pair of sneakers to put them in. Also, I used very comfortable cotton socks that had some cushioning in them. That helped alot. I bought moleskin too (not real moleskin btw) also sold by Dr. Scholls to help my feet.
I would advise not bringing new shoes or wearing anything you can't walk around alot in comfortably. Also, take breaks, and if possible, put your feet up. That will help.