If wired the way you suggest the breaker would have to protect the outlet and the entire subpanel. The breaker and the outlet would have to match.
There is no useful combination of breaker/outlet/subpanel that could work this way.
You can't run say a 60A subpanel off a 60A breaker and put a 20A outlet on the feeder cable.
If you use a 15A breaker and a 15A outlet, you don't need a subpanel, you could just run more 15A outlets along the same circuit. Same with 20A.
If you use, say, a 50A breaker the outlet must be 50A. Then, if it's allowed you could continue to a 50A subpanel. (I don't think that's allowed anyway). You could only attach a 50A device to the outlet and you could only use it if nothing was running off the subpanel. The whole arrangement would be pointless.
If you use an even bigger breaker the outlet would have to be correspondingly bigger and then there is literally no domestic device you could plug into it.
You could run the subpanel conduit through a box (it would have to be a larger than usual box) and install an ordinary outlet there but not connected to the feeder cables. Feed the outlet through wires coming back from the subpanel through the same conduit. Would that suit your needs? The need for the box to be larger, and to accommodate the larger conduit meant for the subpanel, might spoil your plans, depending on what they are.