Learn Hardcore Spanish (Spain): El cajón es tan ancho que mi cartera cabe sin problema. - The drawer is so wide that my wallet fits without a problem.

tan + adjective/adverb + que for “so … that …” with adjectives/adverbs: tan ancho que.
tanto + noun + que for quantities of nouns: Tanto espacio que…
tanto + verb + que when “so much” modifies the verb: Corrió tanto que se cansó.

So with an adjective (ancho), it must be tan.

What does que do here? Could it be como? Does it need an accent (qué)?

Here que introduces a result clause: “so wide that…”
tan … como is for comparisons of equality: tan ancho como = “as wide as.”
No accent: que (conjunction) ≠ qué (question/exclamation word).

Where is the “in the drawer” part? Should it be cabe en el cajón?

It’s understood from the first clause and is often omitted after tan … que. You can include it:

…que mi cartera cabe en él / en el cajón / dentro sin problema. All are correct; the original just avoids repetition.

How does caber work? Who is the subject?

The thing that fits is the subject.

Correct: La cartera cabe (en el cajón).
Incorrect: El cajón cabe la cartera. (There’s no direct object.) You can also use pronouns:
No me cabe. = “It doesn’t fit (in my space/on me).”

What’s the difference between caber, entrar, meter, and quedar?

caber: to fit by size/capacity. ¿Cabe la caja?
entrar: to go in/enter. La caja entra por la puerta.
meter: to put/place into. Mete la caja en el coche.
quedar (for fit on a person): La chaqueta me queda bien. Also “to remain/be left.”

Is cabe the right form? Any key irregularities of caber?

Yes. Key forms:

Present: quepo, cabes, cabe, cabemos, cabéis, caben.
Preterite: cupe, cupiste, cupo, cupimos, cupisteis, cupieron.
Present subjunctive: quepa, quepas, quepa, …
Gerund/participle: cabiendo, cabido (progressive is rare: está cabiendo sounds odd). Common idiom: No cabe duda = “There’s no doubt.”

Why sin problema and not sin problemas? Are both OK?

Both are correct:

sin problema (singular) = adverbial, “easily / with no problem.”
sin problemas (plural) = “without any problems.” Meaning is essentially the same; use either.

Why is problema masculine?

Because many Spanish nouns from Greek ending in -ma are masculine:

el problema, el tema, el clima, el programa. So: sin problema, un problema, ningún problema.

In Spain, does cartera mean wallet or purse? Any regional notes?

Spain: cartera = wallet; bolso = handbag/purse; billetera also “wallet,” less common.
Many Latin American countries: cartera = handbag/purse; billetera = wallet. It can also mean briefcase or portfolio depending on context.

What’s the difference between cajón, caja, gaveta, cajonera?

cajón: drawer (Spain and widely).
caja: box.
gaveta: drawer (used in several Latin American countries).
cajonera / cómoda: chest of drawers/dresser. Note the accent: cajón (stress mark because it ends in -n and is stressed on the last syllable).

Could I say El cajón es lo suficientemente/bastante ancho como para que mi cartera quepa?

Yes. Pattern:

lo suficientemente/lo bastante + adj + como para que + subjunctive Example: El cajón es lo suficientemente ancho como para que mi cartera quepa sin problema.

Why is it indicative (cabe) after tan … que and not subjunctive (quepa)?

tan … que introduces a factual/result clause, so the indicative is standard: …que mi cartera cabe…
Subjunctive appears with structures like como para que, para que, or when expressing non-factuality, doubt, or purpose.

Can I say …que cabe mi cartera instead of …que mi cartera cabe?

Yes, Spanish allows subject–verb inversion, especially after que. Both are grammatical; …que mi cartera cabe is the more neutral order.

Why ancho (not ancha)? Could I use amplio?

Agreement: cajón is masculine, so ancho (masc. sg.) agrees with it.
ancho = wide (dimension). amplio = roomy/spacious; also fine, with a nuance of “spacious.”