- A Garmin watch, and I'd reluctantly also say an Apple Watch (HRM, SpO2, ECG).
- A bicycle
- A comfortable pillow and mattress
- A CO2 monitor. I discovered my house regularly has very high levels of CO2 (2500+). We now open windows whenever we can and turn on the circulation fan.
Air fryer - Handy for french fries, roasting a couple of peppers, reheating food like pizza slices turns out better than the microwave.
A lot of people I talk to about spending $800-1K on a chair rebuke the very idea; while they themselves are on their second or third IKEA MARKUS ($300/per); while offering a far worse user experience in the interim. Depending on where you live, there's also an unusually large supply on the used market due to telecommutting.
There's a saying: "Spend money on what separates you from the ground." Meaning shoes, beds, and chairs. But I'd also say a desk that is supporting your hands, wrists, and arms should maybe count. Standing desks can help a lot with sitting too long in one position, in particular if your work has times when you don't need to type you can switch to a non-traditional handheld mouse (e.g. ELECOM Relacon), and stand more naturally.
YMMV of course.
A few added bonuses: the app I use for weightlifting (https://www.hevyapp.com/) has an Apple Watch mode, freeing me from my phone during workouts. I can also use the watch to track runs, as mentioned by the commenter in this thread with the Garmin Watch.
I am addicted to my phone like most people, so that smooth, smooth frame rate really makes a difference when you have 8h average screen time every single day.