[sushiboat]

How about a magic shop that sells magic items and summoned creatures? Every turn, some of the unsold items and creatures would drop off the inventory, and new ones would be added. Most RPG games have a magic shop, though I don't think it is common in war/strategy games. In addition to adding an element of random fun, the magic shop might also collect information about the relative demand for different items and units.

Here is a possible game description:

The Mage Guild

The Mage Guild is devoted solely to advancing the study and practice of magic. It is an independent international organization, with a branch in every nation's capital. Although each nation is suspicious of an organization not under its control, the Mage Guild is tolerated because its scholarly activities benefit the training of new mages. The Guild sells magic items and summoned creatures at reasonable prices.