Being busy all the time is bad for you, your team, and your organization. It is far better to allow for slack, which is not a bad thing, but creates opportunities for improvement without needing to schedule them.
“Recipe” for what to work on next, incorporating slack:
- Can you help progress existing planned, started work?
Work on that. - Can’t do that?
Find bottleneck and help work to release it. - Can’t do that either?
Do some (improvement) work which- won’t create any work downstream,
- will improve future throughput, and
- can be paused as soon as existing kanban related work is available.
A bit more reading related to slack.