How to retrieve all data from a subcollection of all document

[VincentCauch]

I am using flutter for my app, I want to retrieve all document (not only for one user) of a subcollection and display in the app. This is how I store in firebase:

String createAt = DateTime.now().millisecondsSinceEpoch.toString();

var ref = FirebaseFirestore.instance
.collection('Trips')
.doc('userId')
.collection('Baggage')
.doc(createAt);

FirebaseFirestore.instance.runTransaction((transaction) async {
transaction.set(ref, {
'departure': city1.text
'destination': city2.text
'weight': _weightcontroller.text,
'id': userId,
'departureDate': date.text,
'username': firstname,
"timestamp": createAt,
});
});

I also have subcollection Cars:

var ref1 = FirebaseFirestore.instance
.collection('Trips')
.doc('userId')
.collection('Cars')
.doc(createAt);

How to retrieve data from subcollection 'Baggage' for all users

Thank you.