Slightly bigger than rear wedge rest shown above by hawkeye69, is this one that I use....
This one allows me to use it in multiple ways. Forwards, backwards, on it's side, flipped over (for a little more height), or on its back for maximum height (and I've used it in all these ways!). I've also used it sideways with the rifle butt laying sideways across the ears. I recently stole some filling out of one of my very large sandbags to tighten it up a bit and give it a little more height. I don't remember when or where I got it from but, I've had it for years and it serves me very well. I have that same one hawkeye69 pictured as well. It's lower, and I use it so infrequently that I keep forgetting that I have it.
I also have a few of the larger ones like Hawkeye69 pictured above. I find that I don't use them nearly as much. Usually for a new rifle before installing a rail.
Tom