Originally Posted by HillRider
The potential problem isn't with the headset, it's with the steering. All that weight (a couple of gallons of milk weigh about 17 pounds) on the bars will have a definite effect on steering response. the general guideline for touring riders is to have no more than 5 pounds in a handlebar bag and less if possible.
As recommended, a rear rack is a better place to carry heavy things and there are even rear racks specifically designed to hold grocery bags.
While I agree that 17+ pounds is too much to mount that high on a bike, that much weight on the front wheel, if carried lower and split between each side, is not detrimental to bicycle handling. Touring cyclist regularly carry that much weight and more on lowrider mounts. It actually improves the handling especially over carrying lots of extra weight on the rear wheel.