We used to be able to make coffee and tea cheaply at work. Then they brought in expensive coffee bars with fancy drinks. That made it pretty expensive for caffeine addicts (that would be most of us!)
So a lot of people started bringing in their own coffee and tea in a vacuum flask. We quickly realized this is actually quite practical - when you have back to back meetings it might be the only way you can get a hot drink. And it's certainly much cheaper than expensive drinks from a coffee shop.
You do need a good vacuum flask though. You do not want one that leaks in your briefcase or only gives you tepid drinks.
Let's find the best vacuum bottle for work.