I love these kind of threads, kinda like getting to go visit a buddy's shop and see how he does things.
The first couple items are made of 3/4" wide micarta for its hardness, for when I don't want any "give".
This one I typically will run lengthwise or diagonal on the blade to ensure there are no low spots. I typically cut a strip of sandpaper and secure one end in the slot on either end then hold the other end.
This one has a little different radius I on each corner and beveled to a sharp edge on one end. Mostly used on plunges, corners and such.
Finally this block is made of hard rubber, I'd guess 75ish durometer, I made it from a trailer floormat. This is the one I typically do most of my finishing with for the "softer" finish Lin mentioned.
I cut my paper into 1"ish wide strips for this sanding "stick" then hold lengthwise and flush on the beveled edge then draw toward myself.