I bought a handlebar bag from Amazon with the clear pocket and a quick release clamp which fits your req. above. (BV Bicycle Map Sleeve Quick-Release Handlebar Bag with Two Mesh Pockets Sold by: BikepakUSA )$30. It seems much better than my M-Wave bag (~$20)where the clamp broke on the first ride.
Adapting a backpack for the front rack does not involve toomuch work. Just cut the coropac panels and burn holes in the bottom panel to match existing holes on the rack top and use appropriate bolts, washers and nuts. The handlebar bag was for another bike. The backpack/front rack is on my MTB/utility bike.