I've seen people drill holes through the top-back part of their boots to run cable locks through them.

I've left my stuff out in the open on long trips, under the principle that: 1) no self-respecting gear thief will want to do anything with my five-year-old textiles that have been soaked through with my sweat, and 2) there is nothing left out in the open that I cannot afford to lose. I had a cable lock securing my drybag with camping gear in it, but if someone wanted to make off with it? It's two hundred euros' worth of gear that I can replace in the next shopping mall. Would I be upset? Sure. Would it completely derail my trip? Nah.

Another bit of philosophy is: if you're off on a walk around the town center, park in the open, as conspicuously as you can. Park right on the main street. Find a place to put your bike where you're not taking up the space that a car could have used, and you're not an obstacle to pedestrians or cyclists. (I like backing into the start or end of a street-parking pocket, a space too narrow for even a Smart car.) Ideally as central and busy a street as possible, right under the watchful eye of a police CCTV camera. In my experience, no parking wardens will bother with an obvious long-distance tourist's bike. And opportunist thieves will think twice about messing with a bike in plain view of the crowd when they are obviously not the biker.

The longer you travel, the more nonchalant you become about it. In rural Switzerland, I just threw my pants and jacket over the saddle, tucked the boots under the belly of the bike, put on my light hiking pants and ten-euro canvas shoes from H&M, and went for a hike in the mountains. It was probably less than wise, but at that point I had stopped caring.