what is your target audience? if its teens the theme of music is usually a good starting point. so u might, for eg. have a sheet that grabs file names from the music folder and extracts title, artist, track etc from the file name.
for oldies parhaps work with a genealogy list and apply functions to pick all the surnames who first names are "John".
for me, i find people more attentive if the theme is related to their own interests because they can take ownership of the content. it often results in more pertinant questions arising from the session because people see applications for the material in their interest area and wonder how to fit the learning to that new application.