Guanciale or pancetta (for carbonara, amatriciana)
Garlic + onion (always)
Dried oregano + basil (for tomato sauces)
Red pepper flakes (Italian style)
Premium dried pasta (De Cecco minimum)
The picks above cover items 1-5 — the foundational items. Add guanciale (Whole Foods or Italian groceries) when you're ready to cook Roman pasta.
San Marzano DOP — The Real Thing
Real San Marzano tomatoes are DOP (Denominazione di Origine Protetta) — Italy's protected designation. They come from a specific volcanic region near Naples, with denser flesh and lower acidity than other tomatoes.
Fake "San Marzano-style" tomatoes are everywhere on US shelves. Verify the DOP label — if it's not there, you're getting US-grown imitations. Cento and La Valle are the most reliable real-DOP brands on US Amazon.
The flavor difference for pasta sauces is substantial. One can of real San Marzano DOP > two cans of any other tomato.
Use Parmigiano for general cooking, ragù, baked pasta, finishing oil-and-pasta dishes.
Use Pecorino for Roman classics: cacio e pepe, carbonara, amatriciana. Using Parmigiano in carbonara is wrong — it's a hallmark of inauthentic preparations.
Have both wedges in your fridge. They're expensive but last months.