Paluumatkan ajan pidän passin ja nousukortin samassa taskussa, etten hukkaa mitään.

Literally, paluumatkan ajan means for the time of the return trip or for the duration of the return trip.

This is a common Finnish time expression:

• paluumatkan = of the return trip (genitive of paluumatka)
• ajan = for the time / for the duration

So X:n ajan means for the duration of X.

Here it means that the speaker keeps the passport and boarding pass together during the whole return journey.

A very similar alternative is paluumatkan aikana. Both work, but ajan often feels a bit more like throughout that entire time.

Because it is part of the expression X:n ajan.

In that pattern, the first noun goes into the genitive:

• paluumatka = return trip
• paluumatkan ajan = for the duration of the return trip

So the -n is not random; it is required by this time expression.

Yes—pitää is a very common Finnish verb with several meanings.

Here it means to keep.

Compare:

• Pidän kahvista. = I like coffee.
• Minun pitää lähteä. = I have to leave.
• Pidän passin taskussa. = I keep the passport in my pocket.

So in this sentence, pidän clearly means I keep, because it has an object (passin ja nousukortin) and a location (samassa taskussa).

They are the objects of the verb pidän.

In Finnish, a singular object in an affirmative sentence is very often a total object, and in many cases that looks like the genitive form ending in -n:

• passi → passin
• nousukortti → nousukortin

So:

• pidän passin ja nousukortin... = I keep the passport and boarding pass...

A useful beginner-friendly way to think about it is: the speaker means the whole passport and the whole boarding pass, not just some unspecified amount of something.

Both words are in the inessive case, which usually means in.

• sama = same
• samassa = in the same
• tasku = pocket
• taskussa = in a pocket

So:

• samassa taskussa = in the same pocket

The adjective and noun match each other in case and number, which is very normal in Finnish.

etten is the combination of:

• että = that / so that
• en = I do not

So etten hukkaa mitään literally looks like that I don’t lose anything, but in natural English it is usually best translated as:

• so that I don’t lose anything
• so I won’t lose anything

In this sentence, it gives the purpose of the action: the speaker keeps the documents together in order not to lose anything.

Yes. That would also be correct.

• etten hukkaa mitään
• jotta en hukkaa mitään

Both can mean so that I don’t lose anything.

The version with etten is compact and very natural. A learner should recognize both patterns.

Because the clause is negative:

• en hukkaa = I do not lose

In Finnish, negative clauses often use the partitive for words like anything:

• hukkaan jotain = I lose something
• en hukkaa mitään = I don’t lose anything

So mitään is exactly what you expect after a negative verb here.

Because Finnish often leaves possession unspoken when it is obvious from context.

If someone says:

• Pidän passin ja nousukortin samassa taskussa

it is naturally understood to mean my passport and my boarding pass, because those are the relevant documents the speaker is carrying.

Finnish does not always need to say my as often as English does.

They are very close in meaning, and in this sentence either would work in many contexts.

• hukata = to lose, misplace
• kadottaa = to lose, misplace

A rough feeling is that hukata can sound a bit like lose through carelessness or mislay, but the difference is not huge here.

So etten hukkaa mitään means so that I don’t lose anything / misplace anything.

Yes. Finnish word order is fairly flexible.

The sentence starts with Paluumatkan ajan to highlight the time frame first:

• Paluumatkan ajan pidän passin ja nousukortin samassa taskussa...

You could also say:

• Pidän passin ja nousukortin samassa taskussa paluumatkan ajan...

That is still grammatical, but the emphasis changes slightly. The original version foregrounds during the return trip.

Yes.

It is made from:

• paluu = return
• matka = trip / journey

So paluumatka literally means return trip or journey back.

Finnish uses compound words very often, and this is a very typical example.