Nomu (=to drink) -> Nomi (present form)
mono = thing
=> nomimono = thing to drink (shortly: drink).
nanika = something.
All the translation thing is adapted for the english users to understand better, whilst the japanese version sounds pretty natural.
If you were to say: atatakai nomimono o kudasai it would translate as hot drink please. Sounds natural in english, but has more of a harsh meaning in jp. By adding nanika to mean "something", in jp the sentence has the same meaning, but is a lot softer and gentle. However, when it comes to the english translation, it doesn't sound natural anymore to translate it word by word, thus the translation being something hot TO drink.
Hope this helps :).
If you still didn't understand properly, I'll try and rephrase my explanation a bit.