The boxer was determined to pack a punch, although he knew that competing with the best national boxers was not easy.
This just means that the boxer was determined to go ahead and PUNCH! PUNCH! PUNCH! Yes, he was all set to pack a punch !
So, the phrase pack a punch literally means to be able to punch powerfully .
The phrase, by extension, also means to have a swift and powerful effect or impact.
So, when the film review reads, “Akshay Kumar packs a powerful punch in the movie,” it means that Akshay Kumar’s role in the movie is very impactful .
The book packs a huge emotional punch that will leave you winded means that the book has a huge emotional appeal.