Spider-Man and Hulk - two of the classic figurehead characters who haven't ever shared any screen time together.
Dr Strange, Hulk and Valkyrie
De-aged Robert Redford, Michael Douglas and Michelle Pfieffer
Ant-Man and Spider-Man
Spider-Man and Cap where they're both on the same side.
In a film that was, partially, a celebration of the MCU's popularity it would've been nice and fitting if the two characters who, for ppl over a certain age comics fans or not, introduced Marvel to the world at large decades ago before the movies had shared a moment onscreen.
Also like others I wanted to see Stark react to Wakanda/Shuri.