A sandbag is great tool for strength and conditioning workouts. You can do almost any barbell lift with a sandbag, and the shifting of the sand will help you work your stabilizer muscles. Working out with a sandbag will also help your grip tremendously.
Also, various moves can be practiced to simulate MMA moves. With a sandbag, you can try ground and pound, positioning techniques, and work some lifts and slams into your routine. A sandbag is great for any combat sport athlete or anybody who wants to get into great shape.
The best part is a sandbag is relatively cheap AND easy to make, a quick trip to the hardware store and a short afternoon of putting it together and you are ready!
Ross Enamait from rosstraining.com has detailed an excellent sandbag construction guide
Ross covers getting the materials, construction, and even details how you can make your sandbag easily adjustable.
If you want more precise gear and have the budget for it check out some training dummies:
Training dummies different weights and sizes starting at $199 bucks