That's not a Ziploc bag, but the retroreflector's dust cover. Here is a larger image of it removed:
And here's an image with the cover still attached to the retroreflector:
The clue is in the use of the red markings along the edges of the part in question, in spaceflight commonly used to indicate parts that need to be removed before use.
Both images from Wikipedia on Apollo Lunar Surface Experiments Package, credit NASA History Office's Apollo Lunar Surface Journal.
I wasn't able to find what the covers were made out of, but they appear to be clear PVC (Polyvinyl chloride). PVC doesn't do terribly well in space and exposure to UV radiation, thermal cycling and sputtering due to exposure to high energy radiation. Cover's current state is of course unknown, but it's a safe bet that it is by now nothing more than a thin layer of dust covered by more lunar surface dust moved around by photocharging, bombardment by hard and particle radiation,...