！
Oh, I'd love a cold beer!
Literal
Cold beer [subject-が] want-to-drink [emotive-なあ]!
~たいなあ is an expressive wish ending: ~たい (want) + なあ (emotional/wistful sentence-final particle). なあ softens the statement into a heartfelt sigh of longing. Classic 'end of a hot day' phrase.