Two settings on Order: Extras control it (both default No):

• Extras: Show on the Cart Preview Page - Yes adds an extras strip below the cart items so customers can add extras without leaving the cart.
• Extras: Add a Popup on the Cart Preview Page - Yes opens a pop-up when the cart page loads, asking the customer whether they want extras, with the same extras strip inside it.

Both need the Extras module active and at least one extra available for the selected date. Extras: Show Popup on Every Load has no code that reads it anywhere in the application - the pop-up already opens on every page load whenever the popup setting above is on, so this row currently has no effect.