I've ridden Vashon Island a couple of times with friends now.
It's a hilly 2,000', elevation gain, 31-mile ride with two options to extend it another 2.5 and 10 miles.
I've annotated a map and created a simple cue sheet (
link), and this is a route that you can upload into your bike computer or smartphone (
link).
There are other places to rest safely and other food opportunities, both noted, but Burton Coffee Stand (20 miles) and
Snapdragon Bakery & Cafe (26.5 miles) are an essential part of the experience, especially when taking a respite from the weather.