I would love to own enough minatures, but when you say "mass combat" I think more than the dozen-of-a-kind that I have.
Though I did get a big pile of warhammer plastic minis last summer in preparation for a need in my game...
Counters (such as the Counter Collection) are very useful, and can be easily marked to have numbers. When the player says "I do 12 pts to Orc #4" it helps the GM, rather than "I do 12 pts to this one here, and the GM has to figure out which of his scratch notes that represents."
For more "one-shot-baddies" things I've used pennies and the like.
John