One of those ideas you wish you'd thought of! GSI's Commuter Java Press ingeniously combines a cafetiere with an insulated mug, making freshly brewed coffee on-the-go incredibly quick and simple.
The outer mug contains the coffee, then instead of the usual rod-plunger, an inner mug with a mesh screen squeezes down inside. This eliminates gritty bits of coffee creeping round the edge of the screen and getting into your brew, and the resultant double-skinned mug helps to insulate it, along with the neoprene sleeve which also provides a soft, secure grip.
Once filled, you'll have to try pretty hard to spill it: the slim profile fits into car cupholders, the non-slip rubber foot helps keep it firmly planted wherever you put it, and the screw-on cap is fitted with a slosh-resistant flip-up lid to drink through. Don't lose a drop of your precious brew!
Although it may be made for coffee, it's perfect for use with tea leaves too.