When I first started touring, I was was super paranoid about things getting lifted from my bike. I have Ortlieb panniers, a 42L hiking backpack as my tail bag and a tank bag. But, as time wore on I realized that really day to day, nobody is going to go explore your bags as you wander into into a store or coffee shop, as long as you park smartly. Interestingly, park it where there's a lot of foot traffic in and out and you can see the bike from inside the store. Having lots of people around is quite the deterrent to thieves. Also, don't ride at night. When I'm stopping for the night at a cheap grungy motel, I usually bring my bags in. If I'm staying with someone and it's a nice neighborhood, I usually just leave it strapped to the bike. I've got a disc lock and a cable lock around someplace to lock the bike up at night. If it's someplace really sketchy but I'm parking to go take a piss or eat, I'll often just bring my tank bag in, which has the easy to filch valuables.