Motor oil and oil filter. I only use mobil 1 and their extended life filter.
Edit to add: I don't know of any shop that will use that oil/filter so I do my own oil changes and even with the "expensive" oil (5 qt. jug from walmart is about $29 and free delivery) it is much cheaper to diy this than have it done.
ETA: Just looked up that price and I was off by $2 so updated it to $29.
I'll run the cheapest oil I can find but I will only buy Mobile 1 filters. I can't remember the YouTube video I watched but the conclusion was Mobile 1 were almost the best and Fram are crap.
It took me a while to land on the mobil 1 filters. I think I was using wix before. Glad to hear they're good.
I assume you change your oil often? I only do so every 5k with the mobil 1 oil ( extended mileage). That still makes me a bit nervous but no problems. The (haynes?) manual I use says not to go more than 5k even with synthetic.
Edit to add: Those videos where they open the oil filters are really interesting. So much marketing bullshit on the outside and very real differences on the inside.