I want something cold to drink right now.

Literal

I [topic-は] now, something cold drink [subject-が] wanted.

欲しい (ほしい, 'wanted, desired') takes が for the desired thing — the same が-marking pattern as 好き/嫌い. 何か冷たい飲み物 ('something cold to drink') — 何か ('something') + 冷たい ('cold') + 飲み物 ('drink').