What did Lehi and his family eat during their eight-year trip to Bountiful?

Raw meat

And so great were the blessings of the Lord upon us, that while we did live upon raw meat in the wilderness ... And we did sojourn for the space of many years, yea, even eight years in the wilderness. And we did come to the land which we called Bountiful. 1 Nephi 17:2-5

Apparently they didn't use fire until Nephi began to build the boat that would take them to the New World.

And it came to pass that the Lord told me whither I should go to find ore, that I might make tools.

And it came to pass that I, Nephi, did make a bellows wherewith to blow the fire, of the skins of beasts; and after I had made a bellows, that I might have wherewith to blow the fire, I did smite two stones together that I might make fire. 1 Nephi 17:10-11

Until then, God made their food taste sweet without cooking it.

For the Lord had not hitherto suffered that we should make much fire, as we journeyed in the wilderness; for he said: I will make thy food become sweet, that ye cook it not; 1 Nephi 17:12