I need protein any time I'm over four hours or so, and unlike running, my stomach can tolerate most anything on the bike. Tuna salad sandwiches are high on my list - just about any convenient store has them.

I think maybe your needs on the bike are related to what your diet is like the rest of the time. Most people don't seem to have an issue with getting enough protein on the bike (judging from what my companions usually eat and what's offered on organized rides). But going only by what you read in the papers, "most people" eat tons of protein every day. I only know what I eat, and that I really have to work to get 50 grams of protein a day without resorting to protein powders.

It doesn't sound like you drank enough either, but that wouldn't cause the post-ride depletion you're talking about.

I can't drink premix Gatorade or anything with HFCS when I'm exerting myself, either. That stuff just messes with my stomach and my ability to absorb real food.