Sandbag Getups (SB GUs) are similar to Kettlebell Turkish Getups (KB TGUs). All "get-up"-style exercises are multi-joint, multi-planar, and hence...very functional. They have been deemed some of the best core movements.
A lot of our guys are using SBs these days. They are really easy to construct and affordable ($25). Check out this video by Rob Shaul of Military Athlete to see how he makes his SBs.
For now, try a few SB GUs with a bag of dog food, laundry, or water softener salt you might have lying around the house. Most of our guys can manage a 40# bag, building up to an 80#er. Women should start lighter.