Besides salmon, what other meats can be grilled on a cedar plank

That white stuff is albumen, the same protein that makes the white of chicken eggs. The albumen is part of the salmon's blood, which means that your fillet was fresh. A trick for dealing with it was developed by Bruno Goussault while collaborating with chef Michel Richard from Citronelle in DC: soak the salmon pieces in an ice cold brine. The article in the New York Times that told the story recommends soaking the salmon fillets for ten minutes in a 10% brine (by weight). To make the brine, dissolve three tablespoons of Kosher salt for every cup of ice cold water and make as many cups as you need.

Buy a cedar plank. Soak it in salted water for a couple of hours

Rub the salmon with olive oil and season it with a little bit of salt, I use kosher salt or smoked sea salt but regular table salt will work just fine. Then put the salmon on top of the plank, skin side down. Then put the plank on the BBQ. You can see the fish cook, it will get pinkish-white starting from the skin and traveling up. If your grill has a top, close it and cook for about 20-30 minutes. Check it to make sure it's not drying out. Internal temp should be around 130 or so.