private String a = "";
private String b = "";

public MyClassA(String a, String b) {
    this.a = a;
    this.b = b;
}

MyClassA myClassA = new MyClassA("a", "b");
Intent intent = new Intent(this, ParcelableActivity.class);
Bundle bundle = new Bundle();
bundle.putParcelable("key", myClassA);
intent.putExtras(bundle);
startActivity(intent);

getIntent().getParcelableExtra("key");