Off the top of my head:

Chair

Standing Desk

Redundant Network Connection / VPN / Better Home Network

Noise cancelling headphones / earbuds

Cheap laser printer

Power protection

Thunderbolt dock.

Enough charger ports so everything can charge at the same time overnight.

UPS if needed. Sized to cover your network gear also, unless you're going to tether to your phone during an outage. Personally, if my neighborhood lost power and I had to work, I'd head to a cowork spot or coffee shop.

Sound deadening if you have roommates, young children, or loud pets. It's not just for telemeetings if you are easily distracted.

PC-related:

Mouse, Keyboard, Dual Monitors.