Which events show up on the visitor timeline out of the box?

With auto tracking on you get a lot for free. The common ones you will see on a profile are sessionStarted, pageOpened, pageLoaded, productViewed, cartAbandoned, audienceMatched, and slotPersonalized. There are also context auto events like campaignDetected and locationDetected that show up as the visitor arrives, so you can tell where they came from and roughly where they are.

None of that needs code beyond having the SDK plugged in with track on.

Worth adding that anything you send yourself lands on the same timeline. So the manual events like goalCompleted, orderPlaced, checkoutStarted, and the generic eventOccurred interleave with the auto ones in chronological order. You do not get two separate lists, it is one stream per visitor with both mixed in by time.