I'm glad I grew up a bit between now and then.
Set 5 banners in a battlefield in a mission
Open a treasure chest
Complete a mission with the Perfect rating
Weaken a hood grappling zombie with 1 weapon, then quickly switch to another weapon to finish it off with one shot
While stopped during a task, don't let a single zombie reach your vehicle's hood
Give George some wolfram.
Give Dave some sand.
Give Dave some money for his project.