hit_test.dart

class MyMetaData {
  // Whatever you want
}

// In the hit test target, e.g. drag target
return MyParentTree(
  child: MetaData(
    metaData: MyMetaData(...),
    child: MyChildTree(),
  ),
);

// In the callback where you hit test; e.g. in the drag update
final hitTestRect = getHitTestRectFromSomewhere();
final HitTestResult r = HitTestResult();
WidgetsBinding.instance?.hitTest(r, hitTestRect);
for (final HitTestEntry hte in r.path) {
  final target = hte.target;
  if (target is RenderMetaData) {
    final metaData = target.metaData;
    if (metaData is MyMetaData) {
      // Do stuff with the found MyMetaData
      // E.g. trigger the drop to the target
    }
  }
}