They mention building a shelter with walrus hides so I'd imagine they did a fair amount of hunting rather than trying to bring all their supplies with them from the outset. Shackleton's voyage used a similar approach.

At this period in time, before Vitamin C was discovered, fresh meat, in particularly raw meat, was critical for survival. The canned food didn't contain vitamin C so scurvy was a constant problem.

The competent explorers learned the habit of eating raw meat from the inuits.

That said, the walrus hut was built by Nansen and Johansen after leaving the ship.