I have had a vintage red five-year diary by Leathersmith before. It was one of my favourites as the cover was sturdy enough to last ages, and the paper was nice and thin. I use these types of diaries for all kinds of things – journalling, blog post scheduler, notes about students, recipes, passwords, travel diaries, meal planning. They are small with strong clasps so very portable and light. Because of the low price (usually between €5 and €10) you don’t have to use them all the way to the end.
I recently found this one on eBay. I have no idea what I am going to use it for, but they don’t come up for sale often, so I decided to go for it.