If you buy pre-made guac from the store, just be sure to check the ingredients and make sure it doesn't have added trans fats or other artificial ingredients.
So at 79 cents, I stock up like a mad woman and make everyone eat guacamole until they're blue in the face (no wait, that would be green in the face...) Buying pre-made guac is always an option, but those scary preservatives are not my thing.