Usually, I don't do these things. Lately, I've bought some things that were quite cheap, but improve life immensely. These are five recommendations on the top of my head.
(Of course, prices may differ depending on where you are living)
An infusion bottle with a straw.
I bought some garbage quality similar bottles before. But the Ikea one is actually the best. Also, it's only €5.
You can easily drink 2-4 liters each day thanks to this.
Invest a teapot where you have a filter and can pour lots of water into it. Those small teapots are useless cause they can only fill probably only two-three small cups of tea. Buy a bigger one, and drink more tea. Once again, you can easily drink 2-4 liters each day thanks to this.
I bought mine in a random store for like €10 and can pour roughly around half a liter or more each time.
You can probably buy a monitor lamp for like $35 to $100. But a desk lamp works just as well if you need to save up some money. It helps your eyes and lights up the mood. I bought mine at Ikea for around €15.
Microfiber cleaning cloths.
Please use these instead of regular tissues or worse... wet wipes to clean your monitors and camera lenses. They also push of dust and keeps your screens and mirrors clean. You can order them very cheaply for around $10-$20.
Candle with a calming scent.
Not sure if it is ever validated, but candles with scent regularly helps me with headaches, stress, or even feeling too tired. When I have one of those emotions, I sometimes light one up and after a while, I feel more relaxed. Here they are around €20,- so not too expensive I think.