If you want to land on Santa Cruz, here's a link for applying for landing permits:
Some of the anchorages are deep and tricky and pretty much all will have quite a bit of open exposure, so high confidence in ground tackle is a good thing.
A dinghy with a reliable motor would be useful.
San Clemente and San Nicholas are distant and restricted (military). If anchoring out, be sure you are fully legal, including all safety equipment, and aware of restrictions.
In case of emergency (medical, inclement weather, etc.)
contact the following at SCI: "Control Bravo" on Channel 16 or San Clemente Island Security at (619)524-9214
also, Naval Base Ventura County - San Nicolas Island