1)Something that is so easy/unchallenging that one does not need to worry about it. Especially relevant when referring to academic school tests/quizzes.
2)Something that requires little prepared effort.
A: Was the Pre-Cal test easy? I've been freaking out about it all morning.
B: Don't worry. It was easy trash.
A: I forgot to do my homework. I'm screwed.
B: Easy trash. You can finish it in less than two minutes.