Guarda el resguardo en la cartera, no sea que te lo pidan otra vez en la ventanilla.

Here resguardo means a receipt, claim slip, stub, or proof of payment/registration—basically a document you may need to show later.

In Spain, resguardo is often used for:

• a bank receipt
• a document proving you submitted something
• a collection slip
• a temporary proof while you wait for the final document

So it is not just any receipt in the shopping sense; it often suggests an official slip or proof.

Guarda is the tú imperative of guardar, meaning keep, put away, or store.

So Guarda el resguardo means:

• Keep the receipt/slip
• Put the slip away

It is a command directed at you informally.

Related forms:

• tú: guarda
• usted: guarde
• vosotros: guardad
• ustedes: guarden

So the sentence is speaking to one person in an informal way.

Yes. In Spanish, subject pronouns are often omitted because the verb form already tells you who the subject is.

So:

• Guarda el resguardo = You keep the slip
• Tú guarda el resguardo is possible, but usually unnecessary

Adding tú would normally give extra emphasis, for example if you were contrasting people:

• Tú guarda el resguardo; yo llevo lo demás.

In this sentence, cartera most naturally means wallet or purse.

In Spain, cartera can have several meanings depending on context, including:

• wallet
• purse
• briefcase/satchel
• even mail carrier in other contexts

Here, because you are being told to keep a resguardo somewhere safe, wallet/purse is the most likely meaning.

No sea que is an expression meaning:

• in case
• for fear that
• lest

So:

Guarda el resguardo en la cartera, no sea que te lo pidan otra vez en la ventanilla.

means something like:

Keep the slip in your wallet, in case they ask you for it again at the counter.

It is a set phrase, and learners should treat it as a chunk.

Because no sea que uses the subjunctive, not the indicative.

• es = indicative, from ser
• sea = subjunctive, from ser

This expression introduces a possibility someone wants to avoid, not a fact. That is exactly the kind of situation where Spanish often uses the subjunctive.

So:

• No sea que... = In case... / For fear that...

You do not usually analyze it literally as may it not be that... when speaking; it functions as an idiomatic expression.

For the same reason: after no sea que, Spanish requires the subjunctive.

• piden = indicative present
• pidan = present subjunctive

The speaker is talking about a possible future action:

• maybe they will ask for it again
• maybe they will not

That uncertainty triggers the subjunctive here.

They stand for to you and it.

• te = to you / from you, depending on context
• lo = it, referring to el resguardo

So te lo pidan means:

• they ask you for it
• literally, they request it from you

Why two pronouns? Because pedir can take:

• the person affected: te
• the thing requested: lo

Examples:

• Te piden el DNI. = They ask you for your ID.
• Te lo piden. = They ask you for it.

Because Spanish object pronouns follow a fixed order. When both an indirect and a direct object pronoun appear before the verb, the indirect one comes first.

So:

• te
  • lo = correct
• lo te = incorrect

The pattern is:

• me/te/le/nos/os/les
  • lo/la/los/las

Examples:

• Te lo doy.
• Me la enseñan.
• Se lo piden.

It is an impersonal/unspecified they.

Spanish often uses a third person plural verb when the exact people do not matter or are obvious from context.

Here, pidan probably refers to:

• the staff
• the clerks
• the people working at the service counter

So it means something like:

• in case they ask you for it again without needing to say exactly who they are.

Literally, ventanilla means small window, but in everyday Spanish it often means a service window, ticket window, or counter, especially in official places.

Common contexts:

• banks
• train stations
• government offices
• post offices

So here en la ventanilla means something like:

• at the counter
• at the service window

This is very common in Spain.

Otra vez means again.

So te lo pidan otra vez = they ask you for it again.

Yes, de nuevo could also work:

• no sea que te lo pidan de nuevo en la ventanilla

In many situations, otra vez and de nuevo are very close in meaning.
Otra vez often sounds a bit more everyday and conversational.

Not very naturally. A word-for-word version would sound awkward.

A rough literal breakdown is:

• Guarda = keep/put away
• el resguardo = the slip/receipt
• en la cartera = in your wallet
• no sea que = in case / lest
• te lo pidan = they ask you for it
• otra vez = again
• en la ventanilla = at the counter/window

A natural English version would be something like:

• Keep the slip in your wallet in case they ask for it again at the counter.

That is a better translation than trying to mirror the Spanish structure exactly.

Yes. Some natural alternatives are:

• Guarda el resguardo en la cartera por si te lo vuelven a pedir en la ventanilla.
• Guarda el resguardo por si te lo piden otra vez en la ventanilla.

A learner should notice that por si is another very common way to say in case.

Compared with por si, no sea que can sound a bit more like:

• just in case
• for fear that this might happen

So the original sentence feels very natural and slightly more expressive.