Joined: Aug 2010
Posts: 12,689
Likes: 2,094
From: Madison, WI
Bikes: 1961 Ideor, 1966 Perfekt 3 Speed AB Hub, 1994 Bridgestone MB-6, 2006 Airnimal Joey, 2009 Thorn Sherpa, 2013 Thorn Nomad MkII, 2015 VO Pass Hunter, 2017 Lynskey Backroad, 2017 Raleigh Gran Prix, 1980s Bianchi Mixte on a trainer. Others are now gone.
I would add one more criteria, estimate how far you might have to go between food resupply and water resupply. If resupply distances are short, not much volume or weight capacity is needed.
When I rode the Pacific Coast, we saw a Safeway about every other day, other food sources (restaurants, convenience stores) much more frequently than that. Thus, did not need a lot of capacity for such expendables. I have no clue how often you can resupply crossing the USA prairie or if taking a southern route how often you can find water, as I have not ridden there.
When I went into the interior in Iceland I brought over two and a half weeks worth of food along, my 31 liter Ortlieb duffle could not hold all the food, I needed another drybag for overflow.