Have any of you seen these at the local auto parts store. Basically they are screwed inbetween the coils of your spring and help with sagging.

I've constantly got a bunch of stuff in my trunk and was wondering if they would be a good fix

 

they stop the spring from compressing. When you go over a bump, the spring is not able to compress, and this transfers more load to the car. NOT a good idea. Go with stiffer springs.