Mein Pass liegt schon im Rucksack, damit ich ihn morgen nicht vergesse.

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Breakdown of Mein Pass liegt schon im Rucksack, damit ich ihn morgen nicht vergesse.

• nicht: not
• morgen: tomorrow
• schon: already

Questions & Answers about Mein Pass liegt schon im Rucksack, damit ich ihn morgen nicht vergesse.

Why does German say Mein Pass liegt (lies) instead of Mein Pass ist (is)?

German often uses position verbs like liegen (to lie), stehen (to stand), and sitzen (to sit) to describe where something is, especially for objects in a certain orientation. So Mein Pass liegt im Rucksack literally means My passport is lying in the backpack, i.e. it’s already in there (typically “lying flat” like papers). You can say Mein Pass ist im Rucksack, but it’s a bit less vivid/specific; liegt is very natural for flat objects like a passport.

What does schon mean here, and where does it go in the sentence?

Here schon means already: My passport is already in the backpack... Its position is flexible, but it typically sits near what it modifies. In Mein Pass liegt schon im Rucksack, schon emphasizes that the passport is in the backpack earlier than the relevant time (before tomorrow / before leaving).
You could also place it as Mein Pass liegt im Rucksack schon, but that sounds marked/less natural in this simple sentence.

Why is it im Rucksack and not in dem Rucksack?