Yeah just go in and ask them if you can take them. Most of the time they don't care. I've gotten many pallets in the past like this. If they say no, just go to the next store.
Very nice props. I especially like your toe-pincher coffin.I am making several props this year with pallet wood. Like Spinwitch mentioned, I got mine free off of Craig's list. They are a pain to take apart as Jaybo stated, they are a pain to take apart. I ended up using a Sawzall with a metal cutting blade to cut through the spiral nails. Once the boards are separated, I use a metal punch to knock out the nail heads.
To screw my props together, I use "Star" drive wood screws. They are self tapping so you don't have to pre-drill the holes. When I got my props assembled, I used a small propane torch to add some more "Aging" to the wood. Here are a few pic of a couple of my pallet wood projects:
Here is a link to my post on them: