As a Denver Print Production Artist, I like to have good resources on hand for use for client projects. Here is a great Print Production Artist mockup resource:
They have lots of great packaging mockups, vehicle wrap mockups, fonts, transparent PNG objects and 3D shapes, and more. This is a great resource for mocking up designs to present to clients. A few of my Ad Agency clients love using this resource for quality Photoshop files that they can mockup art onto. Make sure to add this to your bookmarks.