Leave cash on the table, that's the fastest way to do it.

This is also a great use for bitcoin. Just have the waitress drop a QR code (specific to your party) on the table when you sit down, and you can pay without ever having to flag anyone down, and no need to have an ipad per table or anything expensive and fancy like that, and unlike cash above, no one can swipe the money off the table. That's trivial to do even with current bitcoin technology.