The TV Station News Report
In 'Charlie Don't Surf', after clearing the TV station, you can find a news report playing on a TV screen. It details the events of the coup, providing additional narrative context. It's a small detail but adds to the immersion. Take a moment to listen before moving on.

The 'No Russian' Precursor
While not an easter egg, the mission 'All Ghillied Up' is often seen as a thematic precursor to the controversial 'No Russian' mission in Modern Warfare 2, showcasing the darker, more morally ambiguous side of warfare. It sets a tone for future installments.
Developer Messages
Occasionally, in multiplayer maps or even campaign levels, you might find subtle developer messages or graffiti. These are often inside jokes or hidden signatures from the development team. Keep an eye out for unusual textures or writings in obscure corners.
Compare easter eggs & references inCall of Duty: Modern Warfare II (2022)