My theft-prevention philosophy is that I never leave the bike out of my sight on tour, unless I can safely stash it at a hotel or WarmShowers host first. For example, I do not go into any supermarket. Instead, I only shop from small shops where I can see the bike through the window. When I stop at a restaurant, I either eat outside, or I choose a table inside by the window and put my bike right outside there.
Since I don't leave the bike out of sight, I don't need a serious (= heavy) lock. The cheapest cable lock is enough to deter someone from just grabbing the bike and running.
Personally, I haven't even felt that this approach is a major inconvenience. It comes pretty naturally. But if you are touring with a partner, then of course it is good that your partner can watch your bike while you go inside a large supermarket.