I was able to rely on passing vehicles for water when I was walking along heavily traveled vehicle tracks like F910 and F26.
Food is ludicrously expensive in Iceland, and I was very happy that I brought almost all of mine over from the US. I had to pay an important tax since my food weighed more than the permitted limit. I think the limit was 3kg and every kilogram beyond that was taxed at about $1. Given the price of food in Iceland ($13 for a pint of Ben & Jerry’s) this was an excellent investment on my part.