There's no need to unnecessarily scratch the kayak that you've possibly spent hundreds of hours building and finishing. The rule of thumb "Do not sit in your kayak unless it is in the water" is a safety precaution meant to prevent uneven point loading and possibly damaging (at least cosmetically) your kayak. The same can be said for loading your kayak with alot of gear -- be careful to place your boat on sand or something soft to help distribute the weight while loading and unloading. I will usually place my pfd and maybe spray skirt under my kayak to prevent damage.