What are the ESSENTIAL 1939-1961 Marvel superhero stories?

This is related to my other thread where I said I was gonna read every single Marvel superhero story ever published through the Marvel Unlimited app. Turns out there's still quite a bit that has yet to be uploaded to that app; I found, for example, that there are several quite random issues of [I]Peter Parker, the Spectacular Spider-Man[/I] missing, and the Marvel Max stuff is apparently not allowed. As well as those matters, I've decided that the Golden Age stuff is just too much of a slog to read every single story there is, so I'm gonna just skip right on ahead to the beginning proper of the Marvel Universe with [I]Fantastic Four[/I] #1. But before I do, I wanna make sure there are no [I]essential[/I] stories between 1939 and 1961 that I'd have to stop and look back on in order to understand something post-1961. So what do ya all think are THE most important stories from that era? Obviously, [I]Marvel Comics[/I] #1 and [I]Captain America Comics[/I] #1 are must-reads. But what else?