The Dutch startup behind the Heatbox showed me a near-final prototype at CES 2020. It's a chunky container -- larger than I would typically pack for work -- but small enough to fit inside most backpacks and duffel bags. You'll need to add a smidge of water before you leave the house in the morning, and recharge its 18000 mAh internal battery after three operations. It's activated by a button on the front or through a companion app, which can also be used to adjust the default 8-minute heat time.
I activated the Heatbox and saw some steam slowly rise into the air. The lunchbox was plugged in, though (round-the-clock demos would have been a charging nightmare for the company, otherwise) and I couldn't try any actual food (CES doesn't allow this unless you're an approved caterer, I believe). Still, I could clearly see and feel the heat from the container.
The team raised $90,965 from 581 backers on Kickstarter last November. If you're interested, it's still possible to pre-order one for $144 (it'll normally cost $207) on Indiegogo. As with all crowdfunded projects, there's no guarantee the Heatbox will ever reach your doorstep. I'm hopeful, though, after seeing the company's almost-complete prototype in Las Vegas.