here are the couple of packages that it'll be good to have in the default image:
- System tools: curl wget unzip
- Selenium dependencies: xvfb openjdk-7-jre-headless chromium chromedriver git (maybe firefox and firefox driver as well)
- Database: PostgreSQL latest stable with PostGIS last stable
Maybe also Node.js latest stable
Together with caching it will greatly reduce building time, and taking into account that in one system multiple versions of Node.js and PostgreSQL/PostGIS versions can co-exist there should be no any problems.