At the simplest level, a to-do list is merely a list of tasks that we either think of doing or that some external entity (person, incoming e-mail, thought association, and so on) requires of us. The list is best created in the order in which these thoughts or triggers occur, but it does not follow that they must be handled in the same order.
For example, consider the following list:
Pay bills
Call cable company re: credit for outage
Pick up pants from laundry
Order cake for Aunt Sally's surprise party
Make appointment to have car serviced
Most organizers and planning diaries have places to create task lists, and most personal computers, laptops, and smart phones have provisions for to-do lists. Notepads and index cards may also be used to maintain to-do lists.