Answer:
The expression pack through means putting all in pack-saddles to go faster
Explanation:
This paragraph talks about how the company was trying to get faster to California, they thought that leaving the wagons behind would be a good way since horses would move faster with less weight, is the phrase "preferring not to pack through, made arrangements with Mr. Frink to travel with us. His horse, a good animal, was harnessed to our wagon and proved quite useful." the one that shows that at the end they didn't travel in that way and they continued as the has traveled so far.