Without access to the specific diary entry from the "Diary of a Buffalo Hunter" dated “Nov. Saturday 30 1872,” I can't provide the exact statement that best represents the author's view. However, you can determine the answer by looking for contextual clues in the entry that reflect the author's perspective on buffalo and their significance.
If the entry discusses hunting buffalo for food and sustenance, then "The buffalo are a means for survival" would be the best representation. If it mentions their role in supporting railroad crews, then "The buffalo are a means for feeding railroad crews" would be appropriate.
Pay attention to the author's language and intent in describing the buffalo's use. Test each option against the content of the diary entry to find the best fit.