ashita no bentou ni, onigiri ya yasai o tsumete oku.

For tomorrow’s boxed lunch, I’ll pack rice balls and vegetables in advance.

Breakdown of ashita no bentou ni, onigiri ya yasai o tsumete oku.

• を: direct object particle
• の: possessive case particle
• 明日あした: tomorrow
• に: location particle

Questions & Answers about ashita no bentou ni, onigiri ya yasai o tsumete oku.

What does 明日の弁当 mean grammatically? Is 明日 acting like a noun here?

Yes. 明日 is a noun meaning tomorrow, and の links it to 弁当.

So:

• 明日 = tomorrow
• の = links one noun to another
• 弁当 = boxed lunch / bento

Together, 明日の弁当 means tomorrow’s bento or the lunch for tomorrow.

In Japanese, noun + の + noun is a very common pattern.

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Why is there に after 弁当 in 明日の弁当に?

Here, に marks the destination or container that something is being put into.

So in this sentence:

• 明日の弁当に = into tomorrow’s bento / for tomorrow’s lunchbox

Because the verb 詰める means to pack / stuff / fill, the thing being filled often takes に.

Compare:

• 箱に本を詰める = pack books into a box
• 弁当におにぎりや野菜を詰める = pack rice balls and vegetables into a bento

So に is showing where the food is being packed.

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Why does おにぎりや野菜 take を?