Too many leftovers!
A bad habit in the domain of cooking that I've picked up from being a starving college student is the propensity to cook all of the ingredients I have on hand. Combine this with the fact that vegetables make a lot of food, the fact that you were planning on feeding 15-20 people (but realistically only fed 10), and that Costco has very large portions, and you have a recipe for post-Mystery Hunt leftover disaster.
Specifically, I now have a large pot filled to the brim with stir fried broccoli, chicken, carrots, celery, potatoes and beef chilling out in my refrigerator. It's tasty food (if I may say so myself), but there's only so much stirfry one person is willing to eat... and the quantities here would probably feed someone for a month. Perhaps it is time to invoke the power of living in a dorm.