Spawning bait is the key for early striped bass fishing on Cape Cod. The earliest bait is likely to be herring beginning in May followed closely by herring & mackerel, especially while fishing in Buzzards Bay. Herring fly patterns will be good for the waters of the Cape. In Vineyard Sound there will likely be a good run of spawning squid, so - squid flies will work in varying colors there. As the early season progressess into late May and into June there will likely bite a good bite for weeks and sand eels. I like an olive over white Clouser or a large eel pattern.
My go to flies during this time are the chartruese R2-T2, olive clouser minnow and a large squid fly.