Spray a 13" x 9" baking dish with vegetable spray. Crumble crackers and set aside. Drain vegetables and pour into baking dish. Salt and pepper to taste. Melt butter. Pour half of the butter into the crumbled crackers, then set this aside. Melt Cheese Whiz, then mix in remaining half of melted butter. Pour Cheese Whiz and butter over vegetables. Sprinkle cracker mixture over the top and bake at 350 degrees for 30 minutes.