And I would like advice about the same for travelling ALONE.

When I was in Europe in 1982 I used a simple cable lock, left all the bags on the bike, and left a sign with this pathetic message: "I am 3000 miles from home, and everything I need for survival is on this bike. There is no money, passport, or other valuables on the bike. So please don't steal it."

I did that only a few times, in crowded city pedestrian malls. The rest of the time my fear about having my panniers stolen but a definite damper on my trip, as I refrained from visiting beautiful castles etc.