If you don't mind cooking, I like to pack dried soup: lightweight, nutritious, and after a half-day of canoeing, you probably need the water and salt too.

Both Maggi and Knorr-Swiss make a wide selection of good ones, much better than domestic dried soups like Lipton Cup-o-Soup.  Oxtail and minestrone are personal favourites, but they're all good.

If you're tired at the end of the day (or if you eat your big meal at lunch and want more than a couple of granola bars for dinner), they're substantial enough for a quick meal, especially if supplemented with "nature's bounty" - fresh fish, wild mushrooms etc. Or if you want more calories, you can add extra rice or pasta. (on that note, orzo is the most compact, fastest-cooking pasta that I know of.)