Many of our clients sell mugs, mousepads, etc. with images printed on them.

It can be done by adding the item to the gallery pricing. For example:

Wallet size $10
4×6 $5
5×7 $10
8×10 $15
mug $18
mousepad $12

Although potential customers don’t actually get to see the product, it has worked in the past.

You could also create a page or gallery called Mugs or Other Products and show what the actually product looks like.