Pidän käsimatkatavaran mukana, koska siinä on tietokone ja kirja.

Because Finnish usually drops the subject pronoun when the verb ending already makes it clear who is doing the action.

• pidän = I keep / I hold / I like, depending on context

So Pidän käsimatkatavaran mukana... already tells you the subject is I. You could say Minä pidän... if you want emphasis, contrast, or a more deliberate tone, but neutral Finnish normally leaves minä out.

Not in this sentence.

The verb pitää has several meanings in Finnish, including:

• to like: Pidän kahvista = I like coffee
• to keep / hold: Pidän laukun mukana = I keep the bag with me
• to have to in the structure pitää + infinitive: Pitää lähteä = I have to leave

Here the context shows that pidän means I keep or I keep with me, not I like.

Because it is the object of the verb pidän, and here Finnish uses the total object form.

For a learner, the simplest explanation is:

• käsimatkatavara = basic dictionary form
• käsimatkatavaran = the whole carry-on item as the object

In an affirmative sentence, a singular object that is seen as a complete whole often appears in this -n form.

So:

• Pidän käsimatkatavaran mukana = I keep the carry-on with me

If the meaning were more like an unspecified amount of baggage, Finnish might use a partitive form instead, but that is not what is happening here.

Käsimatkatavara means carry-on luggage, hand luggage, or cabin baggage.

It is made up of:

• käsi = hand
• matka = trip / journey
• tavara = thing / सामान-like item / goods

As a compound, it refers to the luggage you take into the cabin with you, rather than checked baggage.

In context, it can mean:

• one carry-on bag/item
• carry-on luggage in general

Because mukana and mukaan are different forms with different meanings.

• mukana = with, along, in one’s possession; it describes a state
• mukaan = along, with, but with a sense of movement or taking something along

So:

• Pidän käsimatkatavaran mukana = I keep the carry-on with me
• Otan käsimatkatavaran mukaan = I take the carry-on with me

A useful shortcut is:

• -na form: already with you
• -an / -än / -oon / etc. movement form: taking it along

Yes, and many learners will find mukanani easier to understand because it is more explicit.

• mukana = with me / along, when the person is understood from context
• mukanani = with me, explicitly marked by the possessive suffix -ni = my / me

So these are both possible in meaning:

• Pidän käsimatkatavaran mukana
• Pidän käsimatkatavaran mukanani

The second one is clearer for a learner because it spells out with me more directly.

Here siinä means in it.

It refers back to käsimatkatavara. So:

• siinä on tietokone ja kirja = there is a computer and a book in it

This is the inessive form of se:

• se = it / that
• siinä = in it / in that

Finnish often uses a pronoun like this instead of repeating the noun.

Mainly to avoid repetition.

Both are possible:

• koska siinä on tietokone ja kirja
• koska käsimatkatavarassa on tietokone ja kirja

The version with siinä sounds more natural and less repetitive because the carry-on has just been mentioned. English does the same kind of thing:

• ...because there is a computer and a book in it

Because Finnish often uses singular on very naturally in this kind of there is / there are structure, especially in everyday language when the list comes after the verb.

So:

• siinä on tietokone ja kirja = a very natural way to say there is a computer and a book in it

You may also see or hear:

• siinä ovat tietokone ja kirja

That agrees more explicitly with the two items. But the singular on is very common and not strange here.

Because in this clause they are the things that exist in the carry-on.

• tietokone = computer
• kirja = book

Finnish does not have articles like a or the, so the bare forms can mean:

• a computer and a book
• the computer and the book

The context tells you which English translation sounds right. In this sentence, English would usually say a computer and a book.

Yes. Koska introduces the reason.

So the sentence breaks down like this:

• Pidän käsimatkatavaran mukana = I keep the carry-on with me
• koska siinä on tietokone ja kirja = because there is a computer and a book in it

This is a very normal way to join a main clause and a reason clause in Finnish.

It is understandable and basically fine, but many native speakers might slightly prefer a more explicit version such as:

• Pidän käsimatkatavaran mukanani, koska siinä on tietokone ja kirja.

That version makes with me clearer.

If the intended meaning is more like I’m taking the carry-on with me, then another natural option is:

• Otan käsimatkatavaran mukaan, koska siinä on tietokone ja kirja.

So the original sentence works, but small wording changes can make it sound a bit more idiomatic depending on the exact situation.