@wsanders20 thanks for the additional info you sent via email! Knowing that you'll be carrying nearly 35 pounds of canned food, plus your own food, socks, snacks and water, here are a few day packs we'd recommend. Again, fit will be really important to ensure the pack's weight is properly distributed between your hips and your shoulders and to avoid any chafing.
These packs include a 3L hydration bladder and are slightly smaller:
These packs don't include a bladder but are compatible; they are also slightly bigger, which may be necessary for the bulk of your canned food:
Hope this helps - reach out with any additional questions. And good luck with your marathon!