What are some non-violent actions incarcerated individuals could take to protest injustice?

Starvation protests. Hunger strike.

Food strike !

Sing.

Usually educating themselves, to the point that they can essentially do the legal work most of their court appointed attorneys didn’t.

Many cases have been overturned, or at least brought to appeal, from evidence or mistakes found by prisoners.

As the goal of imprisonment, at least in part, is rehabilitation, using the time for higher education can at least make the sentence more than just lost time.

Suicide.

They can call the media, or write a book about the injustice.

Thanks everyone for your suggestions.

^Sorry that they probably weren’t exciting ideas.