Drink your drink before you set off or stop somewhere and have a drink. Cup holders in cars a silly fad that encourages lapses in concentration. When tipping your head back and steering with one hand you are not in full control of the vehicle. Fair play if you are sat in Costa car park but it's something we see on the motorway all the time along with throwing the cup and sandwich wrappers out of the window, really ignorant behaviour.
So where does this bit go then ?
As long as you only sip your tea, it's OK...
(And maintain awareness of what is happening around you, of course. Never reach for the cup if you're not on a straight section of road, for example)
Coffee, though, should be banned completely.
Sure, caffeine gives you a slight boost for a little while... but caffeine is also a diuretic...
So not only do you end up needing to stop more often, to visit the little driver's room... but you end up dehydrated, and that reduces your effectiveness more than the boost increased it.
Those silly cans with pictures of bulls or whatever on them... with even higher levels of caffeine?