The only problem with drinking lots of coffee for the memory is that its not good for the voice....A while ago I wrote out a list of all the songs that I like to sing. Whenever I have time I throw a couple of dice and use them to help me figure out which song on the list I have to sing from memory. Doing that helps keep a lot of songs current and prevents me from falling into a rut where I practice the same few songs over and over. My voice is a creature of habit and I have to keep it on its toes.