Support. Go to a running store and get your hair evanluated, then buy shoes appropriate for your feet. They don't have to be sneakers, but if you have high arches and buy shoes for neutral feet, you're going to hurt. Likewise, if you're a lucky person with neutral feet and you buy a pair of highly structured Vionics sandals, you're probably going regret that, too.
I have high arches and a lot of overpronation. I will be taking two pair of Mixuno Wave Paradox 2 sneakers and two pair of Vionics brand flip flops for our 5 night trip. I do the two pair of sneakers because it takes over 24 hours for a pair to dry fully, and you ALWAYS want to start with dry shoes.
Also, all synthetic socks. Cotton can become abrasive when it gets damp/wet.