You're looking at a brand new product from Quake Inc. called Stack-a-Rest. Think Legos for big boys.
The four interlocking sections of closed-cell foam can be used any way you desire to support a firearm. For example, if you have an AR-15 with an extended magazine, you'd stack all four sections together to provide the necessary clearance when shooting from a bench. However, if you want to drive tacks with your favorite bolt-action rifle, you'd do better to stack three of the sections together to support the fore-end of your rifle, then use a single section under the butt of the gun for a perfect two-point rest.
Stack-a-Rest is great for use in box blind windows, when shooting prone, and anytime you might otherwise try to use your daypack as a rest. (Like you, I've tried to use a daypack as a gun rest only to find I didn't have enough clothing or other stuff in my pack to give my rifle the needed height and support. Frustrating!)
Because Stack-a-Rest weighs only 10 ounces, it's easy to strap to your daypack for use in the field. And in a pinch, it looks to me like you could use it as a cushion when sitting on wet ground; put the pointed side down, Einstein!
From what I can tell, you can't buy this rest online or in stores yet. But I wanted you to know about it now so you can be first in line when it's available.
And if you kill a critter using the Stack-a-Rest, share the pic on our North American Hunter Facebook page because I'd love to see it and then take credit for your success.