I only ever have cafe stops in my ride if I'm with someone, that way one of you can stay with the bikes while the other goes for coffee and cakes. If I can't sit outside within arms reach of my bike then I simply don't stop - no cake, no matter how good, is worth losing my good bike for
When at home my bikes are locked in my man-cave, inside a garage with a steel door that you'd need oxyacetylene to get through
But to be honest a determined thief will always find a way,
I worry about how easy it would be, when cyclists are on a long single track country lane, miles from anywhere and riding alone, for a couple of guys in a van to simply block the road and take the bike from under them
Obviously, in my case there'd need to be several of them, all armed to the teeth and perepared to fight to the death