General:
* A box of candies
* A bag of candies
* A collection of candies
* A variety of candies
* A selection of candies
More descriptive:
* A treasure trove of candies
* A rainbow of candies
* A sweet assortment of candies
You can also use more specific collective nouns depending on the type of candy, for example:
* A jar of lollipops
* A bowl of chocolates
* A plate of gummies
Ultimately, the best collective noun to use will depend on the specific situation and the desired effect.