The two things that I would miss the most if I didn't have them would be Evil Mode (even if my vanilla Emacs keybindings skills are getting a lot better) and the interlocking completion/filtering/sorting/querying/gosh-what-don't-they-do systems of Vertico/Corfu/Orderless/Embark/Marginalia/Cape/Consult.
When I mess up my config and have to use vanilla Emacs to find the silly thing I did, those are what slow me down.
But once you have those (skipping Evil if you're not a Vim user), for IDE-ness you probably want to explore the main major mode packages for those langauges, plus an LSP system (I like Eglot) to give you project-aware completion.
Oh! And if you're a big terminal user, Vterm will give you something powerful, something flexible, and the kind of terminal experience you're used to. You can always explore Eshell later!
Okay, and if you're working with Git, which who isn't, Magit is a must.
Okay, I'll stop before I'm simply listing all the packages I use!
Yeah, you've convinced me... let's not make fun of new people!
... I guess that shouldn't be a controversial stance. Whoops!