For me its velocity, or maybe said as ergonomics. The quicker, and least effort possible to get what I hear in my head out of the speakers the better. Even in studio situations at high dollars, it can have a real effect. The more difficult or inconvenient it is to set up a vocal mic and headphone mix, for instance, the less likely you are to give some new vocal line a try. I like to have all the basics always micd up and ready to go
A decent power conditioner/surge protector for lightening storms (never thought it could happen to me until it did)
Strand lights of some sort (clear C7 globe bulbs for me)
A lava lamp (my wife's contribution - it was hers growing up)
Concert posters on the wall
A clean esthetic for the desk (I have a very simple but very functional, modular, modern DIY desk solution)
A few succulents
Cable management (get a pack of Velcro cable ties from Amazon and go to town - makes such a difference)
Along those lines... get the right cables/stands/etc. for what you need - stop fighting that mic stand that won't hold its position, get a longer cable instead of compromising your layout or stretching your cables, replace that squeaky chair that keeps ruining your takes - you deserve better
Yea - in my case the window is in the wrong place but I'd rather take it and deal with it than leave it. Along those lines, I would like to add small green plant buddies to keep you company. Succulents make good critical listeners.
As @pipelineaudio said the more seamless the expierience
the easier it becomes to create. I also think having a nice
visual environment and comfortable furniture helps one feel relaxed and indirectly enables ideas to flow.
I personally do not like studio environments - machines, acoustic material, a large of windows and sunlight etc...anything I can do to keep the room bright and comfortable is a big win in my book.