I've got a simple setup that makes use of YAML files, Rake tasks, and raw kubectl. I've yet to take a look at helm or spinnaker but it's on my list. You really can go a long way just with K8s' own tooling.
I've started with creating Rake tasks. Then I found https://github.com/CommercialTribe/psykube which is opinionated. Then I've ended up creating my own simple ruby tool to manage kubernetes with my own directory structure and configuration.