Before the age of Kevlar-lined tires, I used 23 mm slicks when touring with only rear panniers. I usually got one flat per tour. These tours typically lasted ten to fourteen days. On its final tour with new tires and tubes, I had no flats. I did not stray from paved surfaces often, but I had no problems when I took the occasional logging road or pebbly country lane.
My new bike has Kevlar-lined tires. I heeded the advice of the bike builder, who recommended that I go for 28 mm tires. I am sure that they are not as zippy as 23 mm tires, but honesty, I do not notice the difference with 8 or 10 kilograms hanging off the bike. I do feel slightly more stable on gravel roads and cobblestones, but I still ride carefully on unsmooth surfaces. My bicycle was designed for touring on roads, not mountain trails.
Kevlar-lined tires are not immune from punctures. I got a flat on the second day of most recent tour while walking my bike along a sidewalk!
Alan