You may get .psd* file of "Golden foil gift box from scratch" Photoshop tutorial by making a payment. Put the tutorial title in "Add special instructions to seller" line of PayPal and it will be sent to you shortly.
- Return to Illustrator document.
- Expand and Ungroup box to get separate sides. (Object > Expand and Object > Ungroup).
You may find separated box in this file.
- Insert box sides into Photoshop.
- Place them above 3d box.
- Leave very small backlashes between sides.
- Corners of the cube should be visible through backlashes.
- Return to 3d box layer.
- Apply Gradient Overlay to it.
- Apply dark gradients to the box sides and make them edges smoother.