I've found two main ones.

The first level is heavily based on WAW's Junglee fighting, such as Marine Raiders going into enemy territory and coming to rescue someone and leaving.

I've also found a quote that's found in Single Player randomly, here it is.

"Damn, thats a Russian block, er what we do know?"

— Southern guy in a Beanie

"Geez, I don't know, hows about you frag the basturds?"

— Some black Sergeant who is very old

Doesn't that sound a lot like this from COD1?

"That's a German, er, roadblock, uh, what do we do now?"

— Elder

"Geez, I don't know! Hows about you try shooting the basturds?"

— Moody