What is the weight of ballistic recovery systems?
The smallest BRS listed here is certified up to 600 pounds (272 kg) of aircraft weight. That should be more than enough for a small jetpack or personal quadcopter. This system weighs about 22 pounds (10 kg), not counting anything required to install it.

As GdD mentioned, altitude may be an issue. The FAQ for a Cessna 182 mentions an altitude loss of about 300 feet, and that is with a rocket deployment.

They make systems for many different types of aircraft and ultralights, some probably smaller than the 600 pound limit listed above. You should contact them if you have a serious interest in such a system.