"They have nothing to drink."
Translation:Nemají co pít.
You cannot just put "nic" in the sentence formulated as the answer above. You can say "Nemají nic k pití.". That is fine and it is an exact word-to-word translation.
The difference is that you can use the with infinitive like "Nemám co dělat."/"I have nothing to do." while you use "k" and the verbal noun "pití" with "nic".