Bringing compiled device to market (and how to power)
Definitely DO NOT dismember the AC adaptor and imbed it in your device.  Use a UL-approved wall-wart power supply (or an iDevice power block) as-is to provide power to your Pi, and provide power to the second device from the Pi box.

If you run 120VAC into your box, you will need regulatory approvals.  The reason so many things use external power supplies these days is so that the device manufacturer doesn't need to worry about UL or similar regulations - the power supply manufacturer takes care of that.