I know what you're thinking to yourself right about now. "That's cool and all John, but are you sure that's really a Pet Sematary promotional item? The cat in the movie was named Church, not Earl!" Allow me to explain...
Earl The Dead Cat is actually a novelty toy that a company by the name of Mad Dog Productions put out back in 1985, with absolutely nothing to do with the movie (obviously, since the movie didn't come out till years later). Dubbed "The last cat you'll ever need", Earl was essentially a plush cat toy, only with most of the stuffing taken out, to make him look like a cat that had spent every single one of his nine lives, and was nothing but a floppy carcass. He came with a humorous death certificate, which listed his cause of death as 'catatonia'. Get it? Cat-atonia?!
Cut to a few years later, in 1989. With Pet Sematary about to be released onto VHS, video rental chain The Movie Exchange had a brilliant idea; since Earl is a dead grey cat, just like the cat in the movie, they decided to order a whole bunch of the toys from Mad Dog, and give them out to customers who purchased the Pet Sematary tape. After getting approval on the idea from Paramount, little Pet Sematary tags were affixed to a bunch of Earl The Dead Cat toys, and many happy families in turn left The Movie Exchange with not only Pet Sematary on VHS, but also a dead cat, for the kiddies. Ah, the 80's!
You can still find Earl The Dead Cat's on eBay from time to time, though the Pet Sematary varieties are pretty hard to come by. I actually saw one not too long ago, amidst an auction of a bunch of other promotional items, but I totally blew the opportunity to win the auction. And it only went for about 12 bucks too. Still kicking myself over that!