Two of my five chew plastic with a passion. One will actually ingest it so I have to be diligent. I'd see tooth marks on my bread bags and napkin packs...whatever was lying around.
Some degree of plastic chewing and other inedible items are fairly common for cats. But when it becomes a problem it can be diagnosed as Pica.
Other ingested items to watch out for would be strings, woolen materials, litter, dirt, paper products....
Pica can be a symptom of other disorders as well (not to panic you!), anemia often being the instigator.
As to why so many cats love plastic no one is certain--perhaps the cool texture? the sound it makes? Some have said that particular animal fats are used in the making of many plastics and that could be the lure? Petroleum products, gelatins...all sorts of weird stuff in plastic.
I just make sure I keep all plastic temptations out of reach. Nothing on the counters, no grocery plastic bags lying around (those are dangers in their own right!). I watch out for strings, as one of my cats doesnt' seem to know when to stop with that....
I always know it's my Frodo chewing leftover plastic that the tissue box was encased in AT FOUR AM in the morning. She is awful! The sound is so irritiating (hairballs still win that contest though).
Basically cats, dogs, and toddlers will eat the damndest things so even if you think "nah, that's safe", think again