I think its a notebook of some kind! I just caught something from the Harold blog post about Cottage living and it says this:
"You will find that this part of town is perfect to have a lot with a garden and space for livestock and oversized crops! You can always take notes as you stroll around the area and see how the townsfolk are doing with their gardens and plots"
This is the second paragraph under the picture of New Old Henford. Maybe this will tie into the errands/tips for gardening?