FOX NEWS has released the contents during ”Week-long National Vacation”, and JFK Jr.'s wife, Carolyn, has posted "10 days?" on her official page of Telegram.
It seems that during the Emergency Broadcast, the Internet and other services will be out of for 10 days.
I suppose that it's gonna be the same situation in Japan, as martial law is gonna be enforced worldwide.
I have heard that during martial law, airplanes and trains will not be able to travel either. There is a possibility that supermarkets will be closed or distribution will be stopped, making it difficult to get food etc..., so it would be better to stock up on food or drinks or stuff you need just in case which if you won't be able to go to a supermarket.
The date of the Emergency Broadcast has not been announced officially, but that's maybe quite possible to be during May 15-25 (US time)