I'd like to propose 'Wood'.  In any shape or form, just wood.

Can I complicate matters and suggest that every 3 months we have a theme that the subjects adhere to?  Eg, 3 months could be nature and the 3 monthly items have to subscribe to that.... next could be, I dunno, mechanics.......or materials..... get the idea?  I know it sounds more complex, but over the long term it would give our competetions a nice 'flow' when looking at all the pictures together......

(",)

When you starve with a tiger, the tiger starves last.