watasi ha sigoto no kaeri ni suupaa ni bangohan no zairyou wo kai ni ikimasu.

When は is used as a particle, it is pronounced wa, not ha. This is a special historical spelling that survives in modern Japanese.

In this sentence, 私は is read わたしは and means as for me. The particle は marks the topic of the sentence.

は marks the topic, while が more strongly marks the grammatical subject or gives emphasis.

So 私は feels like:

• As for me, ...
• I, ...

It sets up the sentence as a statement about the speaker. In a neutral sentence like this, は is very natural. If you used が, it would sound more like you were specifically identifying me as the person who does it.

Yes. Very often, it would be omitted in natural Japanese if the speaker is already understood from context.

So a very natural version is:

• 仕事の帰りにスーパーに晩ご飯の材料を買いに行きます。

Japanese often leaves out subjects and topics when they are obvious.

仕事の帰り means the return from work or more naturally the way home from work / after work.

Here:

• 仕事 = work
• 帰り = return, way back
• の links the nouns

So 仕事の帰り is a noun phrase meaning the way back from work.

This is a very common pattern:

• 学校の帰り = on the way home from school
• 買い物の帰り = on the way back from shopping

In 仕事の帰りに, the に marks the time or occasion when the action happens.

So the sentence means that the action happens on the way home from work.

You can think of it as:

• 仕事の帰りに = when I’m on my way back from work / after work

This に is not marking a destination here. It is marking the situation or point in time in which the main action takes place.

That に marks the destination of 行きます.

• スーパーに行きます = go to the supermarket

So the sentence has two different に particles doing two different jobs:

• 帰りに = on the way back / at that time
• スーパーに = to the supermarket

This is very normal in Japanese.

晩ご飯の材料 means ingredients for dinner.

Breakdown:

• 晩ご飯 = dinner
• 材料 = ingredients, materials
• の connects them

So 晩ご飯の材料 literally means dinner’s ingredients, but in natural English that becomes ingredients for dinner.

The particle の is very flexible. It can show possession, category, purpose, association, and more. Here it shows that the ingredients are connected to dinner.

を marks the direct object of the verb 買う.

The thing being bought is:

• 晩ご飯の材料を = the dinner ingredients

So:

• 材料を買う = buy ingredients

Even though 行きます is the final verb in the sentence, を still belongs with 買い, because the purpose of going is to buy the ingredients.

Because Japanese uses the verb stem + に + 行く pattern to express purpose.

So:

• 買う → stem 買い
• 買いに行く = go to buy

You do not use the full polite form 買います before に行く.

This pattern is very common:

• 食べに行く = go to eat
• 見に行く = go to see
• 会いに行く = go to meet

So 材料を買いに行きます means I go to buy ingredients.

It is a combination of two verbs:

• 買う = to buy
• 行く = to go

But grammatically, the main finite verb at the end is 行きます. The 買いに part expresses the purpose of going.

So the structure is:

• [something] を 買いに 行きます
• go in order to buy [something]

This is why the sentence ends with 行きます even though buying is also part of the meaning.

A useful way to see the structure is:

• 私は = as for me
• 仕事の帰りに = on the way home from work
• スーパーに = to the supermarket
• 晩ご飯の材料を = dinner ingredients
• 買いに = to buy
• 行きます = go

So the pattern is roughly:

topic + time/occasion + destination + object + purpose + main verb

Japanese word order is more flexible than English because particles show each word’s role, but this order is very natural and easy to understand.