Yosef Karo

“ Paragraph 1 - Someone wandering in the desert who does not know when Shabbat is should count seven days from the time he realized that he did not know the day of the week, and on the seventh day he should do kiddush and havdala. If he has something with which to sustain himself, it is forbidden for him to do any work at all until he finishes what he has, at which point he should do work every day, even on the day that he sanctifies [the Shabbat] , in order to preserve his limited sustenance. He is permitted to walk every day, even on the day that he sanctifies. ”