When you're serving more than two cups of coffee, it's obvious you need to use a tray. If you like making things difficult, though, you can opt for these Link Mugs, a set of three coffee mugs that stick to each other so you can carry them with two hands.
In a world without trays, this clever little mug will be King. Since we have trays in this planet, though, I find it just a little bit unnecessary. Not that it's completely useless.
Compared to a tray, Link Mugs makes you look like you're achieving a marvelous balancing feat. Sure, that's not really an enticing benefit, but doesn't it look particularly entertaining? Who knows? A circus scout might be nearby and offer you a job on the spot. Errrr....
Described as "simple and inspired," it consists of individual mugs that can be attached to each other via side connectors (a plug on one side and a receptacle on the other) . You can connect as many mugs as your wingspan can handle, so serving coffee for 15 persons in a single trip to the kitchen should be possible (note: just because it's possible doesn't mean your safety's guaranteed, though - you can trip).
The Link Mugs are designed by Johnathan Aspinall, who has never seen a tray in his life. At least, that's what I suspect. They're available for £32.50 per set.