My 75L backpack proved to be enough for this trip. It has a big zipper opening on the front, which made packing and accessing my stuff very easy. The cover could be taken off to be transformed into a day pack. I used this when I would go into towns when I found a place to leave my big bag for a while. During the part I traveled on bike, I would have this smaller pack on my back the whole day.
Very early in my trip I learned how important it is to keep all gear waterproof. During the first week, I had more rain then all of the other days combined, I think. I was not very well prepared for this. Although my backpack had a rain cover, it did just no hold. My mattress and sleeping bag were soaked because the rain cover did not drain the water well. The bottom of my backpack, which contained my mattress and sleeping bags absorbed it all, leaving me with a wet bed in the night. After this experience I invested in more waterproof bags so everything would at least be protected twice.
While switching to the bike, I needed a bag to fit in the cart. I sought for a cheap weekend bag, but ended up buying a 40L waterproof bag from Edelrid. The best buy I made on the trip. It could easily handle the mud and rain and I needn’t to worry about my stuff inside. The gear inside is the only thing you have, make sure it stays dry and keeps you comfortable during the night. So, whenever you go on a trip, make sure you can handle walking a whole day in the rain. Wet clothes can be pulled off in the night, but sleeping in a wet sleeping bag is the worst you can think of.