I live on the mainland side of Hilton Head and the bass fishing is great down here. However, some of the best fishing is in gated communities and some of those communities are strictly private.
If you go to the Island you can pay a gate fee and get into Sea Pines and there's great fishing in many of the lagoons. My suggestion is to bring or rent a bike and use Google Earth to bike your way from lagoon to lagoon and fish. Keep in mind that you cannot fish on the golf course lagoons and access to many lagoons is restricted because of houses along the water.
Hilton Head Plantation also has good fishing and you can get a pass at the gate to go to Skull Creek and the Old Fort Pub restaurant and then bike to different lagoons. If you park on the road or in the grass off the road in most plantations security will find you and ask you to move your car or have it towed.
Palmetto Dunes has 12 miles of connected lagoons and you can rent canoes or kayaks. However, there will be a lot of tourists paddling around. I also think most of that is brackish water anyway.
Off Island near Exit 8 on I95 is Sergeant Jasper County Park and they have a number of large lagoons. You don't need a fishing license there but there is a daily fishing fee that is around $6. You can also rent kayaks for the larger lagoon in there, but I never had much luck there. There's some decent sized water near the primitive camping area that is about a mile from the main parking lot, so again you may want to bring a bike. I have not fished there yet, but it's somewhere I want to try. I've never heard of 10 pounders in there, but there are 5-6 pounders. There are also tons of lily pads so bring a frog and some heavy braid.
In Sea Pines and Hilton Head Plantation I know of 7-9 pounders landed there, but I don't know the specific lagoons. Keep in mind that small lagoons around here yield big bass as well. Many of the lagoons are interconnected via the stormwater system.
Jarvis Creek Park on Hilton Head is another place to fish, but the biggest I pulled out of there was just over 4 pounds. They also have had issues there with people feeding alligators and we've had gators get aggressive when we have fish on the line. And yes, the gators can get up on the concrete fishing pad there.
Hampton Lake in Bluffton has great fishing but it's a strictly private community. They have stocked their lake with largemouth and tiger bass.
There are also a number of communities that are not private so you can drive right in and fish. However, I would first use Google Earth and historical satellite imagery to see how old those lagoons are. Fishing is usually poor in lagoons less than 10 years old unless the community has an active fishery, and none of the non-gated communities have active fisheries.
There are literally thousands of lagoons around here and most have decent to good fishing, but again a lot are on private communities or private property. If you look at Google Earth there are a ton of lagoons in the woods but you need to be wary of those because we have an abundance of alligators. Personally, I never fish in heavily wooded areas where I don't have a good line of site along the water and a quick egress from the shore. Gators do travel in the woods and the females make their nests and lay their eggs in the woods. Be wary of any large mounds in the woods as it is probably a gator nest. The weather is warming and the gators are getting active. Mating season starts soon so the males will be more active looking for mates.
Also keep in mind that in many cases topwater baits will attract alligators. You can fish them, just keep an eye out.
Anyway, enjoy your trip. Any lagoon you find that's at least 8-10 years old should be holding some bass.