Calendar

To me a calendar is a very basic tool to have with you. As much as we think we'll remember everything we have to do, rarely do we fulfill them all. When you are trying to make appointments for interviews, of any kind, you want to be sure not to over book or double book. When you meet someone and have agreed to meet later you should either confirm it then or if you do the "I'll call you later" then you should mark your calendar to make that call. So many folks don't follow up then wonder why they aren't making the headway they want to make.
Once again, your calendar can be a pocket, hand written type or electronic, that is up to you.