Until today, I have not found a handlebar bag that even holds on very bad roads. But the Ortlieb bag comes close. Of couse it is waterproof.
Somehow Handlebar bags are a contradiction in terms: there is no place on the bike as bad as this to place weight! Never put to much weight here, otherwise the riding behaviour of your bike will get worse. But of course you don't want to miss the practical side of these bags: have the most often used items near by. The map on top of the bag is also indispensable.
For me, the most used item is mainly the camera. To protect it, I made a piece of foam, that fills up the whole bag and only holds the camera. The good side effect is, that I can not put anymore weight in the bag, because it is full this way.