You could use general terms like:
* A batch of cookies
* A plate of cookies
* A box of cookies
Or, you could get creative and use phrases like:
* A scrum of cookies (emphasizing their small size)
* A cluster of cookies (highlighting their grouping)
* A symphony of cookies (if you're feeling poetic about their flavors)
Ultimately, the best collective noun will depend on the context and the image you want to evoke.