We didn't have a problem with fuel on The Rock, but this was due to good management. Each of the Suzukis carried a spare fuel can on the back, giving us a total capacity of around five gallons. We never used the spare fuel, but it was comforting to have in case of emergency. The KLR650 is a supertanker, and Adam did not carry a can.
The general rule is to fill up when one sees a station, even if only a couple of liters down. As one progresses north, the distance between stations increases, and often one has to ride off-route a fair distance to get gas.
87 octane is the norm. While some stations in larger towns have mid-grade and premium, I'd be reluctant to bring a bike that needed high octane. At one station above Gros Morne, we observed a pair of Harley riders pulling up to the pump, only to see that there was regular. They blazed off down the road. If they'd asked, we would have told them that the next station was over 100 km down the road, and had a single pump. They didn't ask.
Photo by Anton