I wonder what movies were most essential to seeing Endgame?
All the Avengers movies are at the top. They showed the relationships the characters have with each other and they're also the movies that are referred to the most.
The Captain America movies help but maybe not absolutely essential? Except for Civil War which I think of as an Avengers movie anyway.
You're probably completely lost on every Guardians scene if you haven't watched the first GOTG movie. Not to mention that it introduces Thanos and the stones. 2nd one is completely unnecessary.
Ironman 2 and 3 are pretty irrelevant I think. Ironman 1 gives a lot of depth to who Tony Stark started out as though.
I haven't seen any of the Thor movies (except the first 1/3 of Ragnarok which I turned off cause it was so bad), and that made me kinda lost a number of times. There were a lot of Thor characters in Endgame who hadn't showed up in any of the previous Avengers movies.
On the other hand, not seeing either Antman movie, Captain Marvel, or Hulk didn't affect me at all.
Black Panther is pretty much a stand-alone movie and not necessary to get Endgame.