Why I need everything in an email.

Something happened this week in one of my classes that I wanted to share and get your feedback on. Last week a student asked if I could bring a cord so they could connect their calculator to a computer and update their OS. 

Student: Did you bring the cord you talked about last week?

Me: No. Did you email me about it like I asked you to?

Student: No.... But I asked you last week.

Me: If it wasn't in an email, I didn't remember.

Student: [Blank stare.]

In general, whenever I talk to a student verbally and they are asking for something, or I need to follow up on something, I ask them to send me an email reminder. With 1-3 such requests each class, for my four college-level classes that adds up to about 4-12 tasks I need to accomplish. To make sure these things are accomplished I use my email as a to-do list, with student emails as the 'things' on my list.

What about you? How do you make sure all the small requests and follow-ups are completed in each of your classes?