The Marvel cinematic universe over the past decade has created an entire cinematic world of 22 movies through which fans all over the world have fallen in love with the different complex but lovable characters starting from Iron Man, Black widow, Captain America to even the newly introduced characters such as Doctor Strange, Black Panther and Spiderman. Where the list of characters seems endless there are quite a number of easter eggs you might just have missed in the Avengers 4 movie.
A disclaimer: Spoiler Ahead, after all: Thanos still demands your silence.
When the the avengers who survived the snap confronted Thanos, before thor cut off his head he also cut off his hand. This is actually quite a recurring theme seen in the Marvel Universe as seen in all the three phases. The main purpose of it being a nod at Star Wars. Characters like Bucky Barnes, Aldrich Killian, Claw and even Groot have lost their appendiges in the past movies. The cutting off of Thanos's arm in fact just continued that theme.
When in the past in New york as the avengers alter the on going events to get their hands on the infinity stones, in one such event Loki escapes with the tessaract. What you might not realize is that there could be reprucussions for such an incident taking place in the main MCU. Even though Tony Stark says that time travelling isnt really like Back to the future i.e. there wont be any changes in the main timeline by altering the past, Steve Rogers when he went into the past and stayed there he aged within the main timeline. That leaves a possibility that the Loki series that have been recently announced might just take place in the main MCU timeline.
When the avengers where in the military base in the 70s, Steve Rogers prank calls young Hank Pym in order to get his out of the laboratory to get their hands on some vials of pym particles so they could go back to the present. Just prior to pym leaving the lab we get in sight an early prototype of the Ant-man helment which was clearly happened to be the classic silver age helmet as seen in the comic books.
One of the most iconic moments of the movie is when Captain America wielded Thors's hammer Mjolnir. We had seen him being able to slightly move Thor's original weapon back in the Avengers movie Age of Ultron which led us to assume that Captain America was the most worthy out of everyone. However, when he summons it in endgame, Thor exclaims saying "I knew it" which suggest that cap had been worthy all along and had just refrained from picking up the hammer out of respect for Thor and that Thor knew about it all along.
The Marvel Cinematic Universe is commonly known for its post credit scenes and so it was almost expected by all that we would again provided with in endgame. However, that did not happen which felt like the Marvel studies trying to emphasize on the end of an era. But there was something as a clanking noise could be heard in the background to a black screen which was actually similar to the noise made by Tony stark while making his first Irom Man suit. What it could actually mean is open to interpretation : from it being an homage to the hero to it being a way of Marvel telling us that it is not the last time we hear or see of Iron Man.