ashita wa kouen de hanami o shinagara, bentoubako ni ireta onigiri o taberu tsumori desu.

Tomorrow I plan to eat rice balls packed in a lunch box while viewing the cherry blossoms in the park.

Breakdown of ashita wa kouen de hanami o shinagara, bentoubako ni ireta onigiri o taberu tsumori desu.

• は: topic particle
• です: to be
• を: direct object particle
• 食たべる: to eat

Questions & Answers about ashita wa kouen de hanami o shinagara, bentoubako ni ireta onigiri o taberu tsumori desu.

Why is 明日 followed by は?

は marks 明日 as the topic: as for tomorrow.

So 明日は does not just mean tomorrow in a neutral dictionary sense; it sets the time frame for the whole sentence. In English, we often just say Tomorrow, ..., but in Japanese, は is very common after time expressions when they are being presented as the topic or contrastive frame.

Compare:

• 明日、行きます。 = I’m going tomorrow.
• 明日は、行きます。 = As for tomorrow, I’m going.

The second one can also carry a slight feeling of contrast depending on context.

Why is it 公園で and not 公園に?

Because で marks the place where an action happens.

Here, the actions are:

• 花見をする = do flower viewing / enjoy cherry blossoms
• 食べる = eat

Those actions take place at the park, so 公園で is correct.

Use に for a destination, existence, or a point of arrival, for example:

• 公園に行く = go to the park
• 公園にいる = be in the park

But:

• 公園で遊ぶ = play at the park
• 公園で食べる = eat at the park

Why is it 花見をする? Why does 花見 take を?