На завтрак я люблю творог с йогуртом, а не сладкую газировку.

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Breakdown of На завтрак я люблю творог с йогуртом, а не сладкую газировку.

• сладкий: sweet
• с: with
• не: not

Questions & Answers about На завтрак я люблю творог с йогуртом, а не сладкую газировку.

Why does it start with На завтрак? What case is завтрак in here?

На завтрак means for breakfast / at breakfast time. After на meaning (for) an occasion/meal, Russian uses the accusative: на завтрак, на обед, на ужин. So завтрак is accusative (and it happens to look the same as nominative for this masculine inanimate noun).

Is На завтрак more like “at breakfast” or “for breakfast”? Which is the best translation?

Both are possible depending on context. In Russian, на завтрак commonly means what you have for breakfast (your breakfast choice), but it can also set the time frame (at breakfast). In this sentence it strongly feels like for breakfast, I like… (i.e., what you choose to eat/drink).

Why is я included? Can it be omitted?

Yes, я can be omitted because the verb form люблю already shows I.

• Neutral: На завтрак люблю творог…
  Including я adds emphasis/contrast: As for me / I personally like…

Why is the word order На завтрак я люблю… and not Я люблю… на завтрак?