There are plenty of services out there that will print your digital photos on caps, mugs and other ephemera. The selling point for Photobox, which recently launched itself in Australia? You can sync with your Facebook account to easily access pictures you have shared on the social networking site for printing.
If Facebook is the main way you store photos, this would save having to go through a separate upload process. (Be sure to deselect the option to let the app post to your Facebook account.) You can choose to upload every album you have stored in Facebook, or just select individual albums. The site points out that older photos in lower resolutions may not print well.
There are also other options for adding photos for printing (including direct upload and sharing from Picasa). Basic photo printing rates are $0.15 per print, which isn't the cheapest option around but isn't ridiculously high either. Currently, users signing up get credit for 40 free prints.