There's a few options.
- In the UI, management -> saved objects -> export everything. This will get searches, visualizations, and dashboards. Index patterns will have to be re-added
- There's a newer API for exporting dashboards, although it's still undocumented. Kibana import/export dashboard api offers some pointers on how to use it.
- At a low level, saving the .kibana index. All kibana state is saved in the .kibana index, so you can snapshot/restore, or use another tool to dump all the documents.