In one interview SW claims that she had originally planned to take an A5 notebook on the walk to make notes, but had decided not to in order to reduce the weight of their backpacks
Picking out this bit, it sounds highly implausible. For one thing, that implies that they coordinated their packing across both backpacks. That would be an obviously sensible thing to do, but given their various conversations about 'did you pack my painkillers?' RW not having a hat and so on, and being surprised when Moth suddenly gets out a radio to listen to the Ashes, all that suggests haphazard packing where neither knew what the other was carrying. Secondly, the radio (only mentioned as being used once!) would weigh a lot more than an A5 notebook, and therefore their packing decisions were badly made and inconsistent. Seems much more likely to me this was an excuse for not making notes as they did the walk.
(Back now after holiday travel break: enjoyed the Observer talk yesterday, didn't add questions as others were covering that ground - get well soon @Uricon2 ! 💐)