To me, that should be illegal without some kind of reuse program.
Dry ice is the solid form of carbon dioxide, though. So when it sublimates, the CO2 will go into the atmosphere.
Jokes apart:
>Plumbers use equipment that forces pressurised liquid CO2 into a jacket around a pipe. The dry ice formed causes the water to freeze, forming an ice plug, allowing them to perform repairs without turning off the water mains. This technique can be used on pipes up to 4 inches (100 mm) in diameter.[23]
Not exactly great for the environment (how does an ice pack manage to have more plastic inside than the entire rest of the packaging?), but yes, you can casually throw them out. Also a brilliant example of marketing and customer deception.
I have no idea where I could drop them for reuse, or how I'd even look that up local to me. Then how many do I need to take in one trip to be make sense, carbon-wise, for me to make the drive over? I bet it's an awful lot, and I don't really have a place to store packing peanuts for 2 years while I accumulate enough to be worth the trip
But if you can, just post an ad on your local classified.
Some Ebayer will gladly jam garbage bags of them into their car.