What foods are sunnah to eat?

The best-known sunnah foods are dates, honey, milk, olive oil, black seed, vinegar, barley and gourd (pumpkin family). These are foods the Prophet ﷺ ate, praised or recommended. Eating them is a nice way to follow his example, but none of them is obligatory.

Dates

Dates were a daily staple in Madinah. The Prophet ﷺ broke his fast with them, ate an odd number before the Eid al-Fitr prayer (Sahih al-Bukhari 953), and said that whoever eats seven Ajwa dates in the morning will not be harmed by poison or magic that day (Sahih al-Bukhari 5445). See What is iftar and how do I break my fast?

Honey and milk

The Prophet ﷺ loved sweet things and honey. The Quran itself describes honey as a source of healing.

يَخْرُجُ مِنۢ بُطُونِهَا شَرَابٌ مُّخْتَلِفٌ أَلْوَٰنُهُۥ فِيهِ شِفَآءٌ لِّلنَّاسِ "There emerges from their bellies a drink, varying in colors, in which there is healing for people." Quran 16:69

Milk is mentioned in the Quran as a pure drink from Allah's creation (Quran 16:66), and the Prophet ﷺ drank it often and made dua for blessing in it.

Black seed, olive oil and vinegar

Black seed (nigella, habbatus sawda): the Prophet ﷺ said it is a cure for every illness except death (Sahih al-Bukhari 5688). Scholars explain this as a general benefit, not a replacement for medicine.
Olive oil: the olive tree is called "blessed" in the Quran (Quran 24:35), and the Prophet ﷺ encouraged eating it and using it on the skin.
Vinegar: he said, "What an excellent condiment vinegar is" (Sahih Muslim 2052), praising even a simple meal of bread and vinegar.

Barley, gourd and meat

Barley: his household often ate barley bread, and he recommended talbina, a warm barley porridge with milk and honey, to comfort the sick and grieving.
Gourd (squash): Anas saw the Prophet ﷺ pick out pieces of gourd from a dish because he liked it, and Anas loved gourd from that day on.
Meat: he ate lamb and especially liked the shoulder, but meat was not an everyday food for him.

The sunnah also includes how he ate: sitting, saying bismillah, eating moderately and never criticising food. See What dua do I say before eating? For what is halal in general, see What can Muslims eat?

A word on health

These foods carry blessing, but they aren't medicine on their own. If you have diabetes, allergies or a medical condition, follow your doctor's advice before adding lots of dates, honey or black seed oil.

Key points

Dates, honey, milk, olive oil, black seed, vinegar, barley and gourd are known sunnah foods.
Eating them is recommended out of love for the Prophet ﷺ, not required.
The way he ate (calmly, moderately, with bismillah) is also sunnah.
Follow medical advice for health conditions.

Tip: Start small: a few dates and a spoon of honey in your breakfast, or olive oil and vinegar on a salad. Say "I'm eating this because the Prophet ﷺ loved it" and it becomes an act of love.