Eu comprei cenoura, alface e carne para o jantar de amanhã.

Yes. In Brazilian Portuguese, subject pronouns are often left out when the verb already makes the subject clear.

So both of these are natural:

• Eu comprei cenoura, alface e carne para o jantar de amanhã.
• Comprei cenoura, alface e carne para o jantar de amanhã.

Including eu can add emphasis, contrast, or clarity, like I bought it.

Comprei is the first-person singular form of comprar in the pretérito perfeito.

Here it expresses a completed action in the past:

• comprei = I bought

It refers to one finished action: the speaker bought those things.

In Portuguese, when listing groceries or food items in a general way, it is very common to use the noun without an article.

So:

• comprei cenoura, alface e carne

sounds like a normal shopping list: I bought carrots/carrots, lettuce, and meat.

If you add articles, the meaning can become more specific, depending on context:

• Comprei a carne = I bought the meat
• Comprei uma cenoura = I bought a carrot

Here, the speaker is just naming the items they bought.

Because Portuguese often uses the singular for food items when talking about them as substances, categories, or shopping-list items.

So:

• cenoura can mean carrots in general
• alface can mean lettuce
• carne can mean meat

If you want to specify number, you would usually use plurals or numbers:

• duas cenouras
• três alfaces
• dois quilos de carne

Their grammatical genders are:

• cenoura — feminine → a cenoura
• alface — feminine → a alface
• carne — feminine → a carne
• jantar — masculine → o jantar

This matters for articles and adjectives:

• a cenoura fresca
• a alface bonita
• a carne boa
• o jantar especial

Both are possible, but they are slightly different.

• para o jantar de amanhã = for tomorrow’s dinner, a specific meal
• para jantar = to eat for dinner / for dinner in a more general sense

Using o jantar makes it sound more like a specific event: the dinner tomorrow.

So this sentence is focused on a particular dinner.

Yes, it is completely normal.

de amanhã literally means of tomorrow, but in natural English it is best understood as:

• tomorrow’s
• for tomorrow

So:

• o jantar de amanhã = tomorrow’s dinner

Portuguese often uses this structure:

• a reunião de amanhã = tomorrow’s meeting
• a aula de amanhã = tomorrow’s class
• o jogo de domingo = Sunday’s game

Also, it is de amanhã, not do amanhã, because amanhã does not normally take an article here.

Yes, in everyday Brazilian Portuguese, that is very common.

• para o jantar → pro jantar

So in casual speech, many Brazilians would say:

• Eu comprei cenoura, alface e carne pro jantar de amanhã.

This is informal and very natural in conversation.
In more formal writing, para o is safer.

Because in Portuguese, the final and in a simple list usually does not take a comma before it.

So this is standard:

• cenoura, alface e carne

That is the normal punctuation in Portuguese.
A comma before e can appear in special cases for emphasis, rhythm, or to avoid ambiguity, but not in an ordinary list like this.

Yes. Portuguese allows some flexibility.

The original order is very natural:

• Eu comprei cenoura, alface e carne para o jantar de amanhã.

But you could also say:

• Para o jantar de amanhã, eu comprei cenoura, alface e carne.

This puts more focus on for tomorrow’s dinner.

You could also omit eu:

• Comprei cenoura, alface e carne para o jantar de amanhã.

That is probably the most natural everyday version.

A couple of useful pronunciation points:

• amanhã has a nasal ending. The final -nhã is not pronounced like English nya exactly; it has a nasal vowel.
• jantar in Brazil usually has a final r that is softer and often sounds like an English h sound in many accents.

Very roughly:

• amanhã ≈ ah-ma-NYÃ
• jantar ≈ zhan-TAH(h) or jan-TAH(h), depending on accent

Also:

• the j in jantar sounds like the s in measure
• the nh in amanhã is like the ny sound in canyon, but with nasalization afterward

The full phrase is more specific.

• para o jantar de amanhã = for tomorrow’s dinner
• para amanhã = for tomorrow

So if you say:

• Comprei cenoura, alface e carne para amanhã

it means the items are for tomorrow, but it does not explicitly say they are for dinner.

The original sentence makes the purpose very clear: the food is specifically for tomorrow night’s meal.