Here are some options depending on the context:
Informal:
* A bunch of buckets
* A pile of buckets
* A heap of buckets
More specific:
* A set of buckets (if they are part of a specific set, like a cleaning kit)
* A row of buckets (if they are lined up)
* A collection of buckets (if they are gathered together for a specific purpose)
You can also use a descriptive phrase to refer to the collection of buckets, like:
* A collection of brightly colored buckets
* A group of buckets filled with sand