There are none. A 1 watt is about the maximum legally allowed. Any more than that presents a serious risk to health. The range is generally a few hundred feet in erfect conditions with NO obstructions between one antenna and the other. In any case, using a company wifi is only legal within the company's prescribed area. For someone like McDonalds this is normally limited to the inside of their property and may just include any external seating area, and then only of you have purchased their food. Otherwise he could be liable to 5 years in prison for theft of service.
Can't be done. The signal usually reaches just outside the door and no further, it's set like that. The idea is that you surf while you eat. Did you think they were a charity? Why not go and ask if they mind you running a cable?