Go to any Eroskis or Aprops on route and pick some food and drink up. Prices at the surrounding bars are very, very high!
I remember when I last did it, I bought a few bottles, and a baguette had change out of 10€, while others were paying the same for just one bottle.
CLothing wise, your outside, so just have your usual clobber on, and at the very least a T-shirt as there can be a breeze dependant on the time of year.