The "Kingdom Report" page, the "City Report" page, and the main screen all show the population and "gold" available, and the "City Report" page indiciates the impact of the amount of food produced in terms of whether it is limiting city growth, but none of these places seem to provide information on the amount of other materials, like lumber, being produced and/or available to the player.  Since these materials potentially impact the choice of which buildings to produce and/or which troops to train, it seems this information should be easily available.

It would seem that either the bottom of the main screen, next to the population and money indicators, should show the amount of other materials available, or the "Kingdom Report" page should show which resources are available in each city to be used for production.