Yes, that's right, a tire. It's truly amazing how great of a workout this one thing can provide you. And no, you don't need a huge tractor tire, just a regular car tire. Most tire shops have old, unusable tires they will let you have for free. After you get one, head out to an empty parking lot or park, and have at it. These exercises will give you plenty of options.
Overhead press: Hold the tire flat, with your elbows even with your shoulders. Press overhead, and slowly return to the starting position. Holding the tire flat will allow your head to fit in the middle so you do not hit yourself.
For increased difficulty, press the tire forcefully and let go, pushing it as high as possible. Be sure to step out of the way. Movements should be powerful, so if you feel like your movements are slowing, or the tire isn't as high, your set is finished.
Backward throws: Place the tire on the ground standing up. Grab the top part with both hands, bending the knees slightly and pushing the hips backward. Forcefully press the hips forward and extend the back, throwing the tire backward overhead as you do.
Twist and throw: Slightly bend both knees, and hold the tire with both hands on the outside of one knee. Forcefully rotate the opposite direction, throwing the tire as far as you can to the side.
Quick side hops: Lay the tire flat on the ground, standing next to it. Jump sideways into the middle of the tire, then out on the opposite side. Repeat this movement back to the beginning. This is one rep. You can do this exercise for reps or a set amount of time.
Long side hops. Lay the tire flat on the ground, standing next to it. For this exercise, jump sideways completely over the tire and back. Again, this can be done for reps or a set amount of time.
High jumps: Stand the tire upright and jump over it. That simple. You can do this facing forward, or, if you're really good, sideways.
Tire drags: Tie a rope around the tire long enough to stand a few feet away with some slack. Hold on to the rope and run forward, backward, or shuffle sideways.