The short answer is: your favorite notebook. The long answer is, use a high quality notebook that will last. You can also purchase the custom Bullet Journal® notebook available from our store. It features numbered pages, an index, a bullet key, 3 bookmarks, an 8-page Bullet Journal guide and more!
The two main things to keep in mind are size and quality. If it’s too big you’ll never take it with you. If it’s too small it will be impractical. Be sure to get something that’s rugged enough to keep up with you. I love that I can refer back to years worth of my old Bullet Journals.