I'm a fan of Bullet Journaling. It helps to categorize, document, and carry tasks, thoughts, and ideas forward, or remove them while making them available for sourcing.
All it takes is a pen and notebook.
All it takes is a pen and notebook.
So far the closest I've gotten is having a Google Doc, but it doesn't have the same flexibility that a hand-written notepad does (e.g. symbols, indexes, ease of writing/ access).
I also have a Samsung Note phone which is useful in the rare case I'm caught without a notebook or pen. I'll re-write any notes to my work notebook as needed.