I believe (i.e., I read somewhere, probably here) that the flags will eventually disintegrate, due to the heavy UV exposure of the nylon material. Based on experience (ever seen a video store with big display windows?), the red stripes will fade before the blue does.
There are undoubtedly other plastic items on the Moon, but I don't know what kind of plastic, or how it reacts to very energetic light.
The metal stuff will probably last until the Sun become a red giant, if not longer.
"For shame, gentlemen, pack your evidence a little better against another time."
-- John Dryden, "The Vindication of The Duke of Guise" 1684