Ideally, you need a dedicated marine system with an underlying soundings and bottom chart. It also should be updatable.
As you will quickly learn, the inlets in SC change shape, and position, with every storm! Only local knowledge will help you there, there can be nothing so destroying as lying on your side with a lee shore, watching your boat get pounded.
I pads won't cut it; they are too delicate, too reliant on signal, and often the charts you see are well out of date.