I've read that people that do long distance touring here in the USA say they can get food usually in 2 days, BUT, they carry 3 days worth in case something happens that delays them like bad weather. Actually the rule is if you know you can travel one day to get to food you should have another day extra, or if you know it will take 3 days to get to food you should have another day. And that doesn't even include the weight of water which you need more than food! So 20 pounds would be quite limiting unless you do what I do and only travel on a weekend to a public camping site.