What additional ingredient is used with vodka and peach schnapps in a Sex on the Beach shot?

In a Sex on the Beach shot, the additional ingredient used with vodka and peach schnapps is cranberry juice. This combination creates a sweet and fruity flavor profile that is characteristic of the drink.

Cranberry juice contributes a tartness that balances the sweetness of the peach schnapps. The inclusion of this juice also gives the shot its distinctive reddish hue.

The other options, such as grenadine, orange juice, and ginger beer, do not complement the primary flavor profile of vodka and peach schnapps in the same way cranberry juice does. Grenadine would add sweetness but lacks the tartness, orange juice would introduce acidity and citrus notes that diverge from the intended flavor, and ginger beer would introduce spice and fizziness, which would alter the overall character of the shot. Thus, cranberry juice is the ingredient that completes the Sex on the Beach shot effectively.