Return to Revisions

For those looking for a simple answer:

1. Use prefix + :, then type in capture-pane -S -3000 + return. (Replace -3000 with however many lines you'd like to save, or with - for all lines.) This copies those lines into a buffer.
2. Then, to save the buffer to a file, just use prefix + : again, and type in save-buffer filename.txt + return.

(By default prefix is ctrl + b.)