@Wintermute21 :D
Paying bills is always helpful.
Even if you don't contribute to an open project in any meaningful way, just having practical experience of using tools like Jira and Github /git; reading existing code; and building it using gradle / maven / ant will put you head and shoulders over almost any other Jr. applicant.
One alternative would be to sign up to github and use it to implement some of the book's examples and kill two birds with one stone!