I use Emacs both on my office desktop computer, on my notebook, and on my phone. Nothing else is really required.
My office machine is a middle class PC with a bunch of RAM. I use only one screen in portrait mode (i miss a second one occasionally, but not as much to get myself another one). On top of that i use Arch Linux, the i3 window manager, and Emacs. Sometimes i use Firefox and a terminal, too.
My notebook is a Lenovo Yoga which can be easily converted to a tablet. It has Fedora on it, and the same i3 and Emacs config as on my desktop.
On my phone i run Lineage OS, Firefox mobile, and Emacs in Termux.
I do almost everything in Emacs now: development (i even run tests in that, and do some live REST API testing, too), task management (Org mode is a really good friend of mine with that), mailing (mu4e), basic browsing needs (eww), company chat (matrix-client.el), some external chats on Slack, and so on. Sometimes i even control Spotify from it.
On my phone i use dedicated apps for these tasks; the screes is too small for a lot of tasks. K-9 Mail for mailing, Orgzly for my Org files (although i often switch to Emacs for that), miniVector for Matrix (a stripped down version of Riot) and the Slack client.
I listen to music exclusively in Spotify, as i can conveniently switch between my computers and my phone.
Pretty much that’s it. For everything else i do i don’t need a computer.