It's January 2013 and my husband and I just spent a week in Hilton Head, in a vacation resort (time share unit). We had a full kitchen. There are tonnes of these kinds of resorts on the island, with kitchens.
For kosher food, I brought from Toronto more than it turned out we needed. You should bring challah (for shabbat), cheese, and any specific favourites. I brought kugel for shabbat along with prepared chicken and rice. There are several supermarkets. We used Walmart (where I purchased some utensils and foil pans), Publix, the Fresh Market (upscale/gourmet). The Publix and Walmart are in the same plaza near Hilton Head Plantation. You probably know what you can find in their regular isles, so here's a not-quite-compete list of what you can find in the Publix kosher shelf and freezer section (back of Isle 9):
-olives, pickles, borscht
-Sabra houmous (in the regular fridges)
-Liberte yogurt (and other brands - but they only had a plain k. The Fresh Market has more selection of kosher ones)
-Pilaf, rice, felafel, latka, kasha, couscous, and taboule box mixes
-cracked wheat, dry beans, dry bean soup mix
-jars gefilte fish, sardines, wasabi sauce
-matzo (of course :)
-fake chicken soup, bag n' bake coating
-marble cake in one of those packages that never go bad so they don't even bother to put a date on them, turkish deliight, sesame candies, halva, tea biscuits
-Empire frozen kosher chickens and turkeys
-Frozen chicken fingers
-Frozen egg rolls, mozarella sticks, and eggplant sticks
-Chopped liver spread
-Frozen gefilte fish rolls
-Puff pastries (e.g., hot dogs in blanket and some others)
I noticed that there is a 'Yo' frozen yogurt place opening up soon, and there might be other such places -- I don't know for sure and I don't know which ones are considered kosher because I'm from Canada...
We don't eat at vegetarian restaurants, but as far as we can tell there is only one restaurant that claims to be vegetarian.
There is one congregation - Beth Yam. It is reform. On their website they tell a bit more about the Jewish community and services.
As of this writing, there is no Chabad.
Hilton Head was absolutely lovely. We lucked out on the weather, so there was plenty to do for a week, even if you don't play golf or tennis. The cheap (no-gear) bike rentals are fine for cruising around and riding along the beach. Try a kayak trip in broad creek, which had plenty of wildlife viewing, and if you're from Canada, don't expect much from the Pinckney Island Wildlife Reserve - they just don't seem to know how to create a wilderness feel around here :). Enjoy!
My husband and I stayed at the Hadassah's B&B for 4th of July weekend. It was a wonderful trip and I would highly, highly recommend staying there. You'll get a huge, hot breakfast every morning plus shabbos meals. There is also a kosher (cholov stam) ice cream shop and bakery in Charleston. The Publix has a wide variety for kosher food you can buy if you decide to cook meals. The B&B has a kosher, dairy kitchen you can use and Hadassah re-koshers it after every guest. We also went to Myrtle Beach on our trip. There is a meat and a dairy restaurant there. Both were pretty good but had odd hours in the slow summer months.