Ich packe meinen Rucksack mit frischem Obst und Wasser.

and

Breakdown of Ich packe meinen Rucksack mit frischem Obst und Wasser.

• das Wasser: the water
• ich: I
• mit: with
• frisch: fresh
• das Obst: the fruit
• mein: my
• packen: to pack
• der Rucksack: the rucksack

Questions & Answers about Ich packe meinen Rucksack mit frischem Obst und Wasser.

Why does mein become meinen before Rucksack?

Because Rucksack is masculine and functions as the direct object of packen, it must be in the accusative case. The possessive pronoun mein therefore takes the accusative masculine ending ‑en, giving meinen Rucksack.

Why does the preposition mit require the dative case for frischem Obst and Wasser?

In German, mit always governs the dative case. Any noun phrase introduced by mit must be in dative. That’s why both frischem Obst and Wasser appear in the dative here (even though Wasser has no visible ending).

Why is the adjective frisch written as frischem before Obst?

When an adjective stands directly before a noun without an article or pronoun in the dative singular, it uses strong adjective declension. For masculine and neuter nouns, the ending is ‑em, so frisch becomes frischem.

Why is there no article before Wasser, and could you include one?

Here Wasser is an uncountable (mass) noun in a general sense, so German often omits the article. If you wanted to refer to a specific water you have in mind, you could say mit dem Wasser.

Why is Obst never plural in this context?

Obst is an uncountable noun in German and is only used in the singular when referring to fruit in general. To refer to individual fruits you’d use countable terms like Äpfel (apples) or Bananen (bananas).

What is the difference between packen and einpacken, and how would I use einpacken here?

packen simply means “to pack.” einpacken is a separable verb meaning “to pack up” or “to wrap/pack for taking along.” If you choose einpacken, you split the prefix and place it at the end:
Ich packe meinen Rucksack mit frischem Obst und Wasser ein.

Why is packe in the second position of the sentence?

German main clauses follow the verb‑second (V2) rule: the finite verb (packe) must occupy the second slot. First comes one element (here Ich), then the verb, then the rest.

Can I also say Ich packe frisches Obst und Wasser in meinen Rucksack, and how does it differ from using mit?

Yes. Using in + accusative (in meinen Rucksack) emphasizes the physical action of placing items into the backpack. Using mit + dative focuses on what the backpack is packed with. Both are correct; the nuance is simply on focus rather than meaning.

How would I say “with my fresh fruit and my water” in German?

You’d decline the possessive pronoun and adjective in the dative:
mit meinem frischen Obst und meinem Wasser
Here meinem is the dative form of mein for masculine/neuter, and frischen takes the weak ending ‑en after the determiner.