Here are some possibilities.
http://www.ccrane.com/antennas/wifi-antennas/
It may be illegal in your state to use someone else’s signal. Do some research on your state.
I just recently bought an iPhone and it was always asking me if I wanted to join this or that Wi-Fi network. Sometimes at a McDonalds or at a Starbucks. Since I don’t even know what they are, I always declined.
AFAIK if the wireless accesspoint is open it may not be illegal.
He said it was a restaurant, and you can guarantee if a restaurant is blasting out a WiFi signal, it’s for the public... LOL...
I’ve been to lots of restaurants that have it... :-)