@wsanders20 what an awesome challenge! We definitely have packs that will be great for walking a marathon carrying 40lbs, but a few things to consider first:
- Will you be carrying anything in addition to the "traditional" marathon gear, like water, food, and an extra clothing layer? Is there anything bulky or oddly-shaped? This will affect the volume of the pack you choose - you can get to 40lbs quickly with really tiny items (meaning the pack can be smaller) or with bigger, bulkier items (which will require a higher-volume pack). Here's an article that may help you hone in on the correct volume.
- Are there any specific weather considerations, like super hot/cold or super rainy? This will impact some features you may/may not want, like prioritizing a really breathable back panel or an integrated rain cover.
- We'd highly recommend a pack with a wider waist belt to help distribute the 40lbs you'll be carrying, so the entire weight doesn't just reside on your shoulders.
- Do you want to use a hydration system or do you plan to carry water bottles? There are pros and cons to both, so if you're not yet decided, this article may help.
- Finally, fit really matters for the duration and intensity of what you're doing, so we'd highly recommend getting fit for this pack - if possible, you can book an Outfitting appointment at your local REI store to ensure a proper fit. If you can't, here's an article that may help you fit yourself.
If you are able to reply here with some of the specifics to our questions above, we'd love to provide a handful of daypacks for you to consider! And good luck with this adventure!