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.
