Chúng tôi không mang nhiều tiền khi đi du lịch, nhưng chúng tôi luôn mang hộ chiếu.

Chúng tôi means we, but it usually excludes the person being spoken to.

• chúng tôi = we, not including you
• chúng ta = we, including you

So in this sentence, the speaker is talking about their group’s travel habit, not necessarily including the listener.

Also, chúng tôi sounds fairly neutral and a bit formal. In everyday speech, people may also say bọn tôi or tụi tôi, depending on region and style.

In Vietnamese, không normally goes before the verb to make it negative.

Pattern:

• Subject + không + verb

So:

• chúng tôi không mang nhiều tiền = we do not carry much money

This is very standard Vietnamese word order.

Compare:

• Tôi không biết = I do not know
• Anh ấy không đi = He is not going

Here, mang means something like carry, bring, or take with you.

In this sentence, it means the travelers have something with them:

• mang nhiều tiền = carry a lot of money
• mang hộ chiếu = carry a passport

English separates carry, bring, and take more clearly than Vietnamese often does. In many situations, mang can cover the general idea of having something with you.

Both mang and đem can sometimes translate as bring or take, but they are used a little differently.

A simple way to think about it:

• mang focuses more on having/carrying something with you
• đem focuses more on taking/bringing something somewhere

In this sentence, mang is more natural because the idea is about what you carry while traveling.

Examples:

• Tôi mang hộ chiếu. = I carry my passport / I have my passport with me.
• Tôi đem hộ chiếu đến sân bay. = I bring the passport to the airport.

In real life, there is some overlap, but mang hộ chiếu sounds very natural here.

Because tiền is usually treated like a mass noun here, similar to money in English.

So:

• nhiều tiền = a lot of money

You do not need a classifier in this structure.

Classifiers are more common when you count individual objects:

• một cuốn hộ chiếu = one passport

But for money as a general amount, nhiều tiền is the normal expression.

Because the subject is already understood from the main clause.

• khi đi du lịch literally means when traveling or when going traveling
• The missing subject is understood to be chúng tôi

Vietnamese often omits subjects in subordinate clauses when they are obvious.

So:

• Chúng tôi không mang nhiều tiền khi đi du lịch
  means
• We do not carry much money when we travel

You could also say:

• khi chúng tôi đi du lịch

But that is less necessary unless you want extra clarity or emphasis.

đi du lịch means to travel, to go traveling, or to go on a trip.

• du lịch relates to travel/tourism
• đi means go

Together, đi du lịch is a very common expression for traveling for pleasure.

Examples:

• Tôi thích đi du lịch. = I like traveling.
• Hè này chúng tôi đi du lịch. = This summer we are going on a trip.

So đi is not unnecessary here; it is part of the normal expression.

Nhưng means but.

It connects two contrasting ideas:

• chúng tôi không mang nhiều tiền khi đi du lịch
  but
• chúng tôi luôn mang hộ chiếu

So the contrast is:

• not much money
• but always a passport

This works very much like but in English.

Because luôn is an adverb meaning always, and adverbs like this usually go before the main verb in Vietnamese.

So:

• luôn mang hộ chiếu = always carry a passport

This is similar to:

• Tôi luôn dậy sớm. = I always wake up early.
• Cô ấy luôn cười. = She always smiles.

So the pattern is very common:

• subject + luôn + verb

Yes, it often can be.

You could say:

• Chúng tôi không mang nhiều tiền khi đi du lịch, nhưng luôn mang hộ chiếu.

That is understandable because the subject stays the same.

However, repeating chúng tôi is also perfectly natural, especially in writing, because it makes the sentence clear and balanced:

• first clause: chúng tôi...
• second clause: chúng tôi...

So both are possible. The repeated subject is not wrong or strange.

Vietnamese nouns usually do not show:

• a
• the
• plural -s

So hộ chiếu by itself can mean:

• passport
• the passport
• passports

The exact meaning depends on context.

In this sentence, the natural English meaning is:

• we always carry our passports or
• we always carry a passport

Because the subject is we, the real-world meaning is that each traveler carries their passport.

If you want to count it, you can say:

• một cuốn hộ chiếu = one passport

No. Khi is very natural here, but lúc can also be used in many cases.

For example:

• khi đi du lịch
• lúc đi du lịch

Both can mean when traveling.

A rough difference:

• khi often sounds a little more neutral or slightly more formal
• lúc can sound a bit more conversational in some contexts

In this sentence, khi đi du lịch is completely natural and standard.