I confess to being a "non-hard core" modeler in this department, as I mostly use N scale Pre-Size and Chooch stone wall materials.
Here's some Pre-Size cut stone chopped up to make bridge piers:

...and some old Chooch random stone wall used for a tunnel portal and retaining wall:

I've used N scale stacked tie retaining wall material that I sliced into narrower strips and bonded back together to make it closer to Z:

For building foundations and suchlike, I laminate leftover etched brass kit walls to sheet styrene to simulate cinderblock:
