Yes, I "open" a set of bookend slices.
Also - mayo on the cheese slice side and mustard or mustard/mayo combo on the ham side. If it's turkey, then it's mayo only.
I used to make them where cheese was on top, but since I discovered Jersey Mike's about 17 years ago and analyzed what they do, it's cheese on the bottom (I still put mayo on the cheese bread).
And yes, cut diagonally. In fact, my wife was making some ham & cheese sammiches for us to eat in the car on Monday while driving to a funeral. She asked me if I wanted mine cut and I said "yes, diagonally", to wit she responded "of course".
Now on a PB&J, I've differed over the years on PB on both sides and jelly in the middle or one and one. But always cut PB&J down the middle.
Now who eats chips piled inside their PB&J? Ruffles, Nacho Doritos, what?