So where I work it’s pretty cold, I do where layers and that does include thermals at times. There is a kettle and microwave at work, however the kettle has bad limescale and the water there is also rather bad. So this means that I buy bottled water, this is usually the cheapest from the supermarket, and I then heat it for cups of tea in the microwave.
As for warming myself I have made heatbags, these I made by cutting old odd socks in half and filling the bottom half with rice and sewing up. I made these before the sewing machine was bought so they are all handsewn. As they are so small they only take 30 seconds in the microwave each, but warm my hands for a while.
My other heating method is a hot water bottle, this I use both the tap water and the kettle for. I also pour the cold water back into the kettle, so I don’t use too much water during the day.
I’ll admit I do kinda wish I could have a lovely warm blanket at work though!