This is my note book, full of ramblings that possibly only I can understand, however it is wonderful for referring back to what I planted, where I brought particular plants, the weather and if I see great ideas online or in books I can jot them down in here and then find them later when I am ready to try them.
Also you would find lots of check lists for jobs to be done, details on how to prune particular plants, flowering dates of the fruit trees and harvesting details. When I notice pest or disease in the garden and any treatments used.
Lots of these things I referrer back to later, it is also essential for planning sowing times and planting times for the next year.
Do you have a garden journal?