Else, I'm so sorry about your cat's addiction. It's tough to get over. Give him all the love and understanding you can. Since he/she isn't able, make sure you throw away directly any plastic you find. I know it's tough love, but ya gotta do it.
Now on a serious side: Your cat may have a blockage from the plastic. That's why he's throwing up. Any food that goes down may not be getting through. Call your vet. Please. Puss needs your help.
Hugs and purrs