Creating a box in Illustrator can be a bit daunting. Thinking and creating in 3D can bend your mind a bit. Here is a simple, easy-to-understand way of creating a 3D box – complete with folding flaps in any form you can imagine. Here goes!
Create a rectangle or square. Add a fill and stroke.
Use the Direct Selection Tool to select one side of the shape.
Use the Down Arrow to move the side of the box and shift it down to create a parallelogram. Create a duplicate of the shape.
Select the duplicate shape and RIGHT+CLICK on it, then choose Transform>Reflect. Reflect the shape vertically to create a mirror image of it.
With the duplicate shape selected, you can pull the shape to any angle or length.
Bring the two shapes together so they meet exactly at the edges. This leaves an odd tanget at the corners where the stroke edges overlap.
To solve this overlap issue, opent the Stroke Panel and do either: Select a rounded corner on the stroke outline OR set the stroke alignment to Inside.
Either of those options will solve the overlap issue.
Duplicate the right side of the box, choose Object> Arrange> Send To Back. Align the back panel to the edges.
Repeat the duplicate steps with the front panel and move it to the back side, then send that shape to the back.
To create flaps, duplicate the side panel, move it up to meet the edge of the side.
Use the Direct Selection Tool to move just the top edge of the flap outward.
Repeat the duplcate panel process around each side of the box.
The flaps can be set in any direction to make it appear partailly open or wide open.
Set the interior color of the flaps to be lighter to make it appear like the light is reflecting off them.
Flaps can be wide open.
Or close all the flaps to make it look unopened.
To create labels on the box, duplicate the sides of the box, hold SHIFT and scale the duplicate panels, then add a different fill/stroke to the shape and this create a perfect label on the panels.