[sosia]

This verb is difficult, because quedar has a lot of meanings, like Tomisimo says.
For me it's reflexive when it's your (or his) own will . It's not reflexive when its something that happens.
Yo me quedo I stay (because it's my decission)
Me quedan $4 ¿Qué puedo comprar? - I've got $4 left, what can I buy? (It happens that I have 4$)
Ella se quedó con ese muchacho - She ended up with that guy. (because it's her decission)
Cómo me queda esta chaqueta? Cómo te queda esa chamarra? - Does that jacket fit me/you? (It happens that fit me?)
Saying "Cómo se me queda" or "como se te queda" its not common, because "se me" or "se te" doesn't sound good.

And the last fact "Se quedó solo en la tormenta" or "Quedó solo en la tormenta" is more a stylish thing.
"Se quedó solo en la tormenta". He stayed alone in the storm. (Own will)
"Quedó solo en la tormenta"". He was alone in the storm. (The fact was that he was alone)
Both says that a person was standing in the stom.
It's better to make it reflexive, because it's the more common option (90% of the time)


Now with the RAE in italic my oppinion


quedar. to be/stay.
(Del lat. quietāre, sosegar, descansar). (Of lat. quietāre, to calm, to rest).
1. intr. Estar, detenerse forzosa o voluntariamente en un lugar.
1. intr. To be/stay, to stop unavoidably or voluntarily in a place.
Always reflexive. Me quedé atrapado por la tormenta. Me quedé de buen gusto. Me quedé dos semanas (It's my own will- or fate's will)
2. intr. Subsistir, permanecer o restar parte de algo. Me quedan tres pesetas. De los manuscritos solo quedan cenizas.
2. intr. To subsist, to remain or to reduce part of something. I have left three pesetas. Of the manuscripts only are left ashes
Not reflexive. It happens to have\left.
3. intr. Dicho de una persona: Ganarse cierta fama o representación, merecida o inmerecida, como
resultado de su comportamiento o de las circunstancias. Quedó como valiente. Quedó por mentiroso.
3. intr. Said of a person: To gain certain fame or representation, deserved or not, as resulting from its behavior or of the circumstances. It stayed as brave. It stayed as liar.
reflexive/Not reflexive. Here it's a fact. At the end all the people think he's a liar. Saying "El se quedó como mentiroso" it's saying he himself made other people think he was a liar. Saying "El quedó como mentiroso" it's saying the same thing but also that other circunstances made other people think he was a liar. So better Not reflexive and you can cover all.

4. intr. Dicho de las rentas u otra cosa que se vende a pregón para las posturas y pujas: Rematarse a favor de alguien. La contrata quedó por Juan.
4. intr. Said of the rents or another thing that is sold announced publicly for the positions and bids :To come in favor of somebody. It contracts was for Juan.
I don't use this form, so no Answer.


5. intr. Dicho de una persona o de una cosa: Permanecer en su estado, o pasar a otro más o menos estable. La carta quedó sin contestar. Quedó herido. Quedó por contestar.
5. intr. Said of a person or a thing: To remain in its state, or to happen to more or less stable other. The letter was without answering. It was wounded. It was to answer.
Here's the fact, so not reflexive. If you thing they had something in the fact, you can put reflexive.
Saying La carta se quedó sin contestar. Se Quedó herido. Se Quedó por contestar. it OK, buit you're emphasizing the fact .
6. intr. Cesar, terminar, acabar. Quedó aquí la conversación. Quedamos conformes.
6. intr. To stop, to finish, to finish. It was left the conversation here. We were in agreement.
The same thing. You can say Se quedó aquí la conversación. Nos quedamos conformes.
7. intr. Ponerse de acuerdo, convenir en algo. Quedamos en comprar la finca.
7. intr. To put itself in agreement, to agree upon something. We agreed buying the property.
Reflexive. You agree.
8. intr. Concertar una cita. Quedamos a las diez.
8. intr. To arrange an appointment. We arranged to meet at ten.
Reflexive you arrange
9. intr. Estar situado. Ese pueblo queda lejos de aquí
9. intr. To be located. That town is far from here.
Not reflexive. It's a fact.
10. prnl. Pasar a la posesión de algo. Yo me quedaré con los libros. . Me los quedaré.
10. prnl. To happen to the possession of something. I will keep the books. I will keep them.
Reflexive.
If it happens to be not reflexive. La herencia quedó para Juan. The inheritance was for Juan
you can also say it reflexive. La herencia se quedó para Juan
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14. prnl. morir ( llegar al término de la vida).
14. prnl. to die ( to arrive at the end of the life).
Both. Juan se quedó en el ataud. Juan quedó en el ataud
Juan remained in the coffin. Juan was in the coffin
15. prnl. coloq. Engañar a alguien o abusar diestramente de su credulidad. Se quedó con Arturo.
15. prnl. coloq. To deceive somebody or to abuse its credulidad skilfully. I deceived Arturo.
Always reflexive. Me quedé con el niño. I deveived the Kid

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It's all my personal oppinion. Hpe it helps
How can I say 90% of the time that happens or something similar??