Thanks for food suggestions - I think I have found something that works for me - cheese sticks and home-made "protein cookies" with whey protein and almond flour instead of wheat flour. (3 g. protein, 4 g. carb, 1 g. fiber, 90 calories.) 2 cheese sticks and 2 cookies give me my 20 g. of protein per meal, plus a few carbs for quick energy. I'm going to try it, anyway.
It only takes me 15 minutes to get to the river, but I have to be there by 5:15.