Eric it would help if you could be more specific in your questions regarding your situation. "how much weight does what to handling". A boat that is designed to accomodate a 200lb paddler plus 75lbs of extra weight won't be as much affected as a kayak designed for a 120#paddler with 75#. A one gallon bottle of water tossed into the farthest aft part of the kayak raises the bow and depresses the stern a little, reducing weather cocking a little. Moving your body forward and aft a couple inches can have as much effect. Lot's of weight, 50#?, distributed evenly sinks you deeper in the water reducing the effects of wind, and also reduces your manueverability. Increasing the gear in the boat will increase the stability. Your question is kind of broad.