Alaska Airlines provides two daily jet flights, and various float plane and air charters also serve the area.
One of the charms of Petersburg is that it doesn't have a deep water port, so it's not accessible by big cruise ships, but some smaller ships stop there. The Alaska Marine Highway provides regular ferry service.
There is a local taxi and some local shuttle services. The local roads are also nice for bicycling, although the size of the island limits the overall distance one can travel.
Le Conte glacier from a distance
Le Conte Glacier - the southernmost tidewater glacier in the northern hemisphere. The glacier moves extremely quickly, offering almost continual calving, including underwater calving leading to "shooters" as icebergs rise rapidly to the surface from the hundreds of feet of submerged ice. Hundreds of harbor seals also inhabit the fjord created by the glacier; closer to the face you're likely to see them lolling about on icebergs.
Whale watching - as Petersburg is located on the south end of Frederick Sound, where many humpback whales summer, it is an ideal starting point for whale watching. Although it's less comfortable to be out on the sound during rougher weather, days with lots of waves are better for seeing aerial displays.
Clausen Memorial Museum has local history exhibits.
Blind River Rapids, mile 14.2 on Mitkof Highway  A boardwalk through the muskeg to Blind Slough, where the salmon are numerous and other wildlife is often visible.
Behind the school there's a boardwalk through the muskeg (extremely soft nutrient poor meadow) that's worth walking.
Because Petersburg doesn't have a deep water port it doesn't get the large cruise ships, thus it isn't overrun with the large cruise line operated tourist shops that plague many such coastal towns. There are a few little locally owned galleries with local artists, and a bookstore with some nice coffee table books, but most of the town actually exists for the local population.
Coastal Cold Storage 1-877-257- 4746 . Assorted fried seafood in a take-out ambiance, but the real treats are the vaccuum packed smoked fish in the cooler.
Morning Mist Bed and Breakfast - Mel and Sherry Stockton are the great hosts.
Water's Edge Bed and Breakfast - the delightful host Barry is a very friendly person.