I try and lessen this risk by making sure that nothing can slide out from under my seat, especially the drivers seat. That way nothing can side under my pedals as I'm trying to control the car or stop.
Behind me I use tie downs etc to hold things in place, and I have just purchased some cargo netting to install as a flexible cargo barrier. (not as good as a solid barrier, but is a compromise for my use)
My 4wd doesn't have a trunk (or boot as its called in Australia). It has a rear door. So I am more conscious of what I put behind me than I have to be if I had a trunk/boot.

Something else to consider is the read folding seat access to the trunk/boot of the car, because if they are not latched quite correctly, or are of poor design, objects can still come flying towards you in an accident. So this can be a false sense of security.