They are charcoal grills at the cabins. Not 100% sure if the trading posts have the charcoal, but I would imagine they do. Prices are high there, however. We bought all our supplies at the Super Walmart on route 192 and saved a lot.
Plan on using around 5# of charcoal per meal (4 people) foil is a good idea since you can drape that over the food to get more of an oven effect. The grills are the typical park style with the adjustable rack.