What a fantastic idea! I'm starting my CPL theory in around a month so this will be very useful! One I learnt for the PPL to help with true/magnetic/compass is the following:
T (True)
-E (take away east variation)
M (gives magnetic)
-E (take away east deviation)
C (gives compass)
Reading it up or down gives a way of converting between the various headings. Simply change to '+' for West variations and deviations.