Google has updated YouYube to let you all add videos to a casting Queue. Next time you have a video playing on the Chromecast connected TV, and there are a bunch of browser tabs open with videos that you want to send to Chromecast after you finish watching the current one, look for + TV Queue. This creates a queue of videos on your Chromecast.
Here is the official YouTube announcement from Google Plus:
Are you casting from www.YouTube.com to your TV and lost in a sea of browser tabs? Good news, matey. Now you can keep playing a video as you browse and queue the next ones to play – all in one tab.
In a post reporting this news, The Next Web says that YouTube i adding Chromecast support to Playlists as well. This is an awesome news (I couldn’t find this mentioned in the official announcement though). I will update this post if I get some kind of confirmation on this.