I am developing skills for Alexa since four months now and really had my bad times with state persistence and state management in my skills. What I've done in the last weeks was to build an SDK for having this done in just a few lines of code. Recently I open-sourced my project. It's got an extensive documentation so feel free to dive into details:
The SDK is an extension for the Skills Kit for Java and it hides all the complexities with saving state to your session or to DynamoDB. It even got a handler for saving state in S3 buckets and provides a framework for letting you build your own state handlers.
The SDK is capable of saving state of POJO models in different scopes (Session, User, Application).
I am really curious of what you think and if you would use it for your own projects.
With some feedback and a bit more testing I plan to publish it in central Maven repo.