asita ha higaeri de umi he iku yotei nanode, ookii suutukeesu ha motte ikimasen.

Here, は marks 明日 as the topic: as for tomorrow or tomorrow in the sense of setting the scene.

So 明日は does not mean “tomorrow” as a direct object or subject. It introduces the time frame for the rest of the sentence:

• 明日は = tomorrow / as for tomorrow

Japanese often uses は after time expressions when the speaker is contrasting or highlighting that time period.

日帰り means a day trip—going somewhere and coming back the same day.

The particle で here indicates the manner or condition:

• 日帰りで行く = go as a day trip
• literally, something like go by means of a day trip / in a day-trip way

So 明日は日帰りで海へ行く予定なので means:

• Since I’m planning to go to the sea/beach on a day trip tomorrow...

Both へ and に can be used with verbs of movement like 行く.

• 海へ行く emphasizes the direction: go toward the sea/beach
• 海に行く emphasizes the destination: go to the sea/beach

In many everyday sentences, the difference is small, and both are natural.

So in this sentence:

• 海へ行く予定 = plan to go to the sea/beach

Literally, 海 means sea or ocean. But in everyday Japanese, when someone says 海へ行く, it often means going to the beach/seaside.

So depending on context, English might translate it as:

• go to the sea
• go to the beach
• go to the seaside

If the meaning was already shown to you as beach, that is very natural here.

予定 means plan, schedule, or intention.

So:

• 行く予定 = plan to go
• 行く予定です = I plan to go / I am scheduled to go

In this sentence, 海へ行く予定なので means:

• since I’m planning to go to the sea/beach

It sounds a bit more definite than just “I might go,” but not as forceful as a firm decision in every situation.

Both なので and だから can mean so or because.

The main difference is tone:

• なので is generally a little softer and more polite/formal
• だから sounds more direct and conversational

Here:

• 海へ行く予定なので、大きいスーツケースは持っていきません。 = Since I’m planning to go to the beach as a day trip tomorrow, I won’t bring a big suitcase.

Using なので fits well with a polite sentence ending like いきません.

Yes, both can work:

• 大きいスーツケース
• 大きなスーツケース

Both mean a big suitcase.

A simple way to think of it:

• 大きい is the regular -i adjective
• 大きな is a special attributive form used only before nouns

In many cases, they are very close in meaning. 大きな can sometimes sound slightly more descriptive or literary, but the difference is often small in everyday use.

So 大きいスーツケース is completely natural.

This is a very common question.

You might expect:

• 大きいスーツケースを持っていきません

That would be grammatically fine.

But は is used here to mark 大きいスーツケース as the thing being contrasted or highlighted:

• As for a big suitcase, I won’t bring one
• implying maybe something smaller is okay

So:

• スーツケースを = neutral direct object marking
• スーツケースは = contrastive/topic marking

In this sentence, は suggests:

• I’m specifically not taking a big suitcase
• perhaps I may take a smaller bag instead

持っていく means to take something along or to bring something (to another place).

So:

• 持つ = to hold / to carry / to have
• 持っていく = to take something with you somewhere

In this sentence, the speaker is going somewhere, so 持っていきません is the natural choice:

• I won’t take a big suitcase with me

If you said 持ちません, it would sound more like:

• I don’t carry / I won’t hold / I don’t have

That does not express the idea of taking it along to the destination as clearly.

The difference between いく and くる is based on direction relative to the speaker’s viewpoint.

• 持っていく = take it away from here / take it with you there
• 持ってくる = bring it here / bring it toward the speaker or reference point

Since the speaker is talking about going to the beach tomorrow, the suitcase would be taken there, not brought here, so:

• 持っていきません = I won’t take it with me

Yes—Japanese often leaves out the subject when it is understood from context.

This sentence does not explicitly say I:

• there is no 私は written

But from the context, the natural interpretation is:

• I’m planning to go to the beach on a day trip tomorrow, so I won’t bring a big suitcase.

This kind of omission is extremely common in Japanese.

Here are the common readings:

• 明日 → あした
• 日帰り → ひがえり
• 海 → うみ
• 行く → いく
• 予定 → よてい
• 大きい → おおきい
• 持っていきません → もっていきません

Full reading:

• あした は ひがえり で うみ へ いく よてい なので、おおきい スーツケース は もって いきません。

It breaks into two main parts:

1. 明日は日帰りで海へ行く予定なので

   • Since I’m planning to go to the sea/beach on a day trip tomorrow

2. 大きいスーツケースは持っていきません

   • I won’t take a big suitcase

So the full structure is:

• [reason] なので, [result]
• Since [reason], [result].

That is a very common Japanese sentence pattern.