On Agency Island, there is a large smokestack only accessible by helicopter or by leaping off the tower. If you jump down into the smokestack, you will land in a large toilet with a few beach balls and golf balls scattered throughout the cave. You need to jump from the top of the tower into this toilet to get the "Pebble Dash" achievement.
In the SportizFreak Lair, there is a shack with a fenced-off area next to it. The fenced-off pen is full of rubber ducks.These ducks cannot be picked up unless you are playing PvP on this map.
Peacekeepers will occasionally yell (referring to the Agent) "He's here to kick ass and chew gum...and he's all out of that...", inspired by a quote from the title character in the 1996 video game "Duke Nukem 3D" and the 1988 Science Fiction film "They Live".