Stripping USB Cable - What to do with shielding?
Both options 1 and 3 are perfectly acceptable for power-only. If you want less noise on the power supply you should probably go with option 1 - tying the shield pins to the ground pin of the USB port. For signalling as well, 1 is the better option.

For power only, bear in mind you should not try to draw more than 100mA without negotiating with the USB host for more. Be sure to factor that in when deciding if the load can be driven by a USB port.