I was never into easter eggs but in these games they are always worth just a timewaster/side mission for yourself so here are the ones I have found. Note: none of the videos i list in this video are not mine they are just used for the purpose of visual representation

So some of you may not know already but to put this out there first there are about 3 or so UFOs in the game some in online some not
That is all you need to know about the UFOs pretty much they aren't good for anything except screenies

This one is more of a side mission than a easter egg but i count it among the many i have found with my friends during my times in gta whether it was online pc or my xbox.
Note: These cannibals will try to kill you in online mode

The first one on this list is the Remains in the Western side of the map. It is kinda hard to find but its kinda cool to explore
Note: Try to use the Kraken Submarine for this part otherwise you might drown

This one took me some time to find but nonetheless i found it on my xbox awhile back. this doesnt confirm that its still there as my friends claim they have seen it. but i reccommend giving it a try even if its not its a great area for screenies and just fun to explore. The bigfoot is from what i can tell pretty hard to find so make sure you have the time and patience.