We have done it a couple of ways: 1) Vancouver to Powell River, across to Vancouver Island, down to Victoria, Port Angelese, Hood Canal, Astoria..........; 2) Tsawwassen, Vancouver Island, Victoria.......
I would recommend the Hood Canal route, rather than the Coastal Washington Route. It is just as scenic (maybe better), and a lot of the road was reconstructed a couple of years ago with good shoulders. Once you hit Oregon there is not a lot of choice for the coast except Highway 101. You won't be very far from stores on any of the Washington and Oregon Route. You can probably resupply every day, with a few exceptions. I don't know about California, but hopefully you can tell us because we are doing that segment next month.
We usually carry one freeze dried dinner as "emergency "rations. If it is used at all, it is because we were too lazy to ride into town or forgot to stop when we passed a market. There is usually enough other stuff in our paniers for another meal in a pinch.