It’s not a pack — it’s a packet. And not THE.

I don’t think anybody actually uses the word sachet. You see it on boxes of tea, but you never really hear people use it.

I did check - several pages of results even in books.

I’m not talking about the existence of the word. I’m just saying it’s an industry word that people don’t actually use when they talk about products. We say packets. 

OK, if you insist. However, ...
"She flipped a sugar sachet between her fingers and said casually ..."
'Yeah, well, you look like –' he points the mangled sugar sachet at me – 'that.'
" I pulled a face at the sugar sachet I was twisting."
"He gave the sugar sachet an angry twist and the flimsy packet gave way."
...

I deliberately ignored authors with odd names.