Good pedal and shoe combination for summer touring
My preference is for SPD clipless pedals and "walkable" clipless shoes.  But I still have a pair of lightweight "tennis shoes" in my gear for campsite, days off, etc.

Another option, if you can still find them, is the old-fashioned "touring" shoes and regular toe straps.  "Touring" shoes are (or were) quite walkable, and it's reasonable to walk miles in them (whereas you'd not like to do that in even "walkable" clipless shoes).

It is a little tricky setting up clipless shoes -- the cleat position needs to be positioned correctly.  Partly this is trial and error (be sure to get your setup early to try it out), but a shop can help you get the right "initial conditions".

(For those who've never seen them, touring shoes look superficially like bowling shoes, with relatively flat, smooth soles, to more easily slip into and out of toe clips.  Unlike bowling shoes, however, the soles are reasonably stiff -- flexible enough for easy walking but stiff enough so that the pressure of the pedal is reasonably well distributed over the bottom of the foot.)