kettlebells are awesome. there's also clubbells, sandbags, medicine balls wrapped in some type of net (i used a basketball hoop once) to slam the floor with, sledgehammers, large truck tires, and wheelbarrows. also i like to use the swingset apparatus at my local park so i can climb up and down the poles when i dont bring rope outdoors.
i've personally never used this, but there's a nifty device called the prowler, which is a lot like a wheelbarrow, but much more gym friendly. i think in the navy fat boy lift, the thing they push and pull is the prowler.