Depends on the situation.

Currently? 40 pound box of cake mix I'm probably going to launch at my store manager.

My cat. Everything else in my room brings me either misery or a feeling of meh. Cat brings joy, which is difficult for me to obtain.

Vibrator.

For almost everyone it's gonna be the phone we're reading this on.

The toilet. Lost count of the number of times this has saved me from getting dysentery or something and it's so convenient when it just pushes the shit away from my house and I never have to see or smell it again. I almost feel bad that I repay it for all its done by repeatedly shitting in it.

Toilet paper 🧻 Very, very useful.

Me? Unless I’m excluded, then the laptop. Although the room itself is pretty useful, but I don’t think I consider it “in the room”.

Me.

Toilet paper

Toilet paper

Outside of my brain and body?

Probably my mobile phone

A 5gal jug full of water. (I don't have AC and it's 32C/90F inside)

The doctor.

The SCADA servers.

I'm in my car.

The car.

Probably my phone, and that probably applies to most rooms frankly if we're talking about potential things I could need to do

That's a tough one because I'm currently surrounded by computers and tools. I'm within reach of my smart phone, one of my laptops, I'm typing this on my desktop PC, I'm within reach of three multitools, a power drill, and my away mission tool bag. So I think I'll give a cop out answer and go with "The several thousand liters of air filling the room."

A human being.

My wife.

The answer is electricity. It's so useful, we take it for granted. Your phones, computers and laptops are not useful if you can't power them.

I'll give the people on the dunny their due: toilet paper is still useful in a room without electricity.

This computer.

I’m in the ER. Probably the doctor standing directly in front of me.

The manager likely thinks it’s him, but it’s actually all the workers that do the work.

Laptop probably. Linux, tmux, i3, vim, GCC, GDB, Pdb, gplaces, links2, curl, wget, netcat, awk, sed... what more could be needed for happiness?

Idunno, but it's preloaded with shittons of tools I don't even know the use of yet (thanks kali). Excluding that probably my lensatic compass. It's nice, quite cheap and not magnetically dampened but it does the job.

Weed

My phone. It might be my laptop, but it's currently not working. If you consider humans, me.

Pumpkin spice old fashioned. With real pumpkin puree!

Most useful? Without a doubt, my laptop. The amount of things that can be done with a modern computer is pretty stunning, and a portable one is arguably more useful.

Other than that, maybe my car keys because the amount of things you can do with a car is stunning, but you need the keys to start it, and the car isn't in this room.

Air freshener.

Air. Can’t go more than a minute or two without it, and there’s enough to share!

Coffee

My pc but that's too easy so I choose my bed as the very next thing. Good comfortable sleep is important.

Towel warmer.

Home server.

Toilet

Computer.

gotta be either the tiny computer i'm typing this on, or the large, sturdy, wooden stick in the corner. if i had to pick to keep just one though, it'd be the phone. a sturdy stick has a million and one uses, but it's also fairly easily replaceable.