البوصلة والمصباح اليدوي بشنطة الظهر.

Because in Arabic, especially in the present tense, nominal sentences often do not use a verb equivalent to is/are.

So:

• البوصلة والمصباح اليدوي بشنطة الظهر = The compass and the flashlight are in the backpack

This is totally normal.
If you wanted to make it more explicit in speech, you could also hear:

• البوصلة والمصباح اليدوي موجودين بشنطة الظهر = The compass and the flashlight are in the backpack

But leaving out are is standard.

Here, بـ means in.

So:

• بشنطة الظهر = in the backpack

In Levantine Arabic, بـ is very common and can cover meanings like:

• in
• at
• sometimes with/by, depending on context

So although a learner may expect في for in, using بـ here is very natural in Levantine.

Because short prepositions like بـ attach directly to the following word in Arabic spelling.

So:

• ب + شنطة → بشنطة

This is normal Arabic spelling.
The same thing happens with other short particles, for example:

• ل + البيت → للبيت
• و + المصباح → والمصباح

So even though in English we separate in the bag, Arabic often joins these small words to the next word.

Because شنطة الظهر is an idafa construction, often called a noun-noun possessive construction.

Literally, it is something like:

• شنطة الظهر = bag of the back → backpack

In this structure:

• the first noun usually does not take الـ
• the second noun can make the whole phrase definite

So:

• شنطة ظهر = a backpack
• شنطة الظهر = the backpack

That is why الشنطة الظهر sounds wrong.

Because they are definite: they mean the compass and the flashlight, not just a compass and a flashlight.

Arabic often marks definiteness with الـ:

• بوصلة = a compass

• البوصلة = the compass

• مصباح يدوي = a flashlight
• المصباح اليدوي = the flashlight

Since the sentence is talking about specific items, both are definite.

يدوي literally means manual, hand-held, or by hand, from يد = hand.

So:

• مصباح = lamp
• مصباح يدوي = hand lamp → flashlight

In this phrase, يدوي is an adjective describing مصباح.

Because مصباح is:

• masculine
• singular
• definite

the adjective also matches it:

• المصباح اليدوي

This is standard adjective agreement in Arabic.

It is understandable and correct, but it sounds a bit more formal/standard than everyday speech in some Levantine contexts.

Depending on the speaker, you might also hear:

• كشّاف
• فلاش لايت

But المصباح اليدوي is still clear and perfectly good Arabic.
So if you are learning, it is a useful phrase, even if some native speakers might choose a more colloquial word in casual speech.

A practical pronunciation would be something like:

• il-boosle w-il-miSbaaH il-yadawi b-shanTet iD-Dahr

A few notes:

• البوصلة is often heard closer to il-boosle
• شنطة is often shanTe
• الظهر is commonly pronounced with an emphatic sound; in Levantine you may hear something like iD-Dahr or iZ-Zahr, depending on the speaker

So the written form is standard Arabic spelling, but the actual spoken pronunciation will sound more dialectal.

Yes. في شنطة الظهر is also understandable and natural.

Compare:

• بشنطة الظهر
• في شنطة الظهر

In Levantine, بـ is very common for location, so بشنطة الظهر sounds quite natural.
Using في is also fine, and may feel more transparent to learners because it maps more directly to English in.

Yes, but the original order is very natural.

Original:

• البوصلة والمصباح اليدوي بشنطة الظهر
• The compass and the flashlight are in the backpack

This starts with the things being talked about, then gives their location.

You could also hear fuller versions like:

• البوصلة والمصباح اليدوي موجودين بشنطة الظهر
• بشنطة الظهر البوصلة والمصباح اليدوي

The second version is more marked and puts emphasis on the location.
For a learner, the original sentence is the most straightforward and natural pattern to use.

It is a mix of standard-looking vocabulary and Levantine-style usage.

Levantine features include:

• using بـ for location
• omitting the present-tense is/are

More standard/formal elements include:

• المصباح اليدوي

So overall, it works well for Levantine, but some words are a bit more formal than what people might use in very casual everyday conversation.