How do I make a body bag that looks like there is actually something in it?

Know anybody you don't like???

Lots!!!! But I think thats illegal!!

A mannequin or a bucky skeleton would be a good start.

I know Frightcatalog has blank bodies. If your really creative, then you could make the bodies yourself out of foam.

You could make body shapes out of clothes stuffed with straw, or that plastic bubble wrap like is used in shipping. 

This should help awsome relults for years of service!

Well that depends...

For an inanimate prop, I think you'd want the random body part sticking out of it. Foam parts or blank cadavers are okay, but you can achieve the same with stuffing old clothes with packing bubbles, foam etc. to give it shape.  You could plant a sound box in the chest cavity to make it 'moan' from injury, too.

Or -- use a REAL person to burst out of the bag!

I saw on e-bay they had blowup figures they were blank no facial features or anything painted on them. different sizes man woman child your choice. If no one is going to see them or pick them up that would work.

take some old clothes and stuff them, dont forget the shoes
use plastic bags for head area
 then wrap in a couple layers of clear plastic  and duct tape around body
or use black bags ..dont forget the tag on bag