I believe they bring a few lengths of line along. Anywhere from 1 - 1.5 X the length of the rod. Line is attached with a quick slip knot so it's an easy swap.
I'm attracted to the simplicity.
mine's a 1975 printing, UK, 2 pounds, got it when I started FF
was fortunate to live in AK for ~10 years, spoiled me
still get out 6-8 times a season, some nice protected trout streams locally (catch/release)
I usually fish by myself, nothing like it
it's a bit more than a hobby imho, between meditation and a religious experience, lol