Wife got me the same 2gal Mr. Beer kit. It opened up a whole can of worms and great hobby. Anyway ....
I've used the PET bottles as a sort of carbing experiment before. To get sparkling, dry cider I used one glucose tab per bottle, but didn't fill the 750ml PET bottle fully. I squeezed the extra air out then capped it. The bottle gives a pinched appearance but as the cider carbs, the bottle fills out and hardens to its original shape. As a matter of fact, I still have one or two 750ml PETs left over from a year ago. Will have to check them out and see if the contents haven't turned into vinegar.
My wife will sometimes use cider I make to cook with. I also make malted and unmalted vinegar from cider The difference is just a bit of wort using crystal malt.