Almost everyone I have met on tour uses a light cable lock combined with a lot of care about where they leave their bikes unattended. A few go with no lock, and ever fewer carry a big heavy lock like you would use in a major city.
I have gone with a very light cable lock on most tours, but have also gone with no lock at all. In places I perceive as high risk I don't let the bike out of my sight. I seldom stay in cities or even large towns preferring to avoid larger cities in favor of rural small towns. In rare cases where I have stayed in cities I usually just got a room. I have wheeled my bike up and down the aisles at walmarts or grocery stores a few times where I thought the risk especially high. I have also taken it inside and parked it in the front of the store a couple times. In small town general stores or diners it is often leaned against the front of the building often not locked.
Many of the towns I stop in have populations with two digits and folks don't lock their houses or cars. I never bother to lock in places like that. I start to consider it a "big city" when the population has a comma in it
At that point I may get more serious about locking or watching the bike.
It helps to ride a bike and use gear that you can easily afford to replace. That reduces the worry greatly. The very worst case I'd be delayed a few days assembling new gear or having it shipped from home on a long tour or maybe ending a short tour. With some minimal attention I think it highly likely I will never have to do either due to a bike theft.
It also helps that I am carrying mostly dirty clothes and used camping gear, on a relatively inexpensive bike, and a minimal amount of those.
Bike friendly cities are the worst since there is usually an established cottage industry of bike theft. Use great care there.
