Nicholas Bate gives us a productivity system so simple it can fit on a single index card.

A fresh 3 by 5 card taken from the stack. One side is work. One side is home. Each side is divided in half with a vertical line. On the LHS side are things you need/have to do. E.g. at work return a client’s call; at home buy some pasta. On the RHS are things you don’t have to do but you will do because they will make your future life easier by reducing the things you have to do on the LHS.

— The Tools of Excellence for a Brave New World, 8: The 3 x 5 card