When an employee has a "reduced" hourly rate due to being considered a "tipped" employee, and the tips plus hourly rate fall below the statutory minimum wage, the employer is required to make up the difference.
So if McDonald's employees get $8 minimum wage and no tips and a Sonic employee gets $5 per hour plus tips, and only averages $2 an hour in tips, the employer has to kick in the other $1, so they both get at least minimum wage, and the Sonic worker might end up with more if people tip well. And in some states, the employer has to pay minimum wage, period, so the tips are extra and the employee gets to keep them (and declare them and pay taxes on them).
So the belief that they need their tips to live is not really based on facts, unless they need more than minimum wage. Since most of them are teens still living at home, minimum wage is probably enough to put gas in their car and cheeseburgers and fries in their bellies, and buy some Itunes now and then -- and dinner and a movie on date night.
I always get the chili cheese dog -- can't eat mayo or onions. yuck. They used to have the Jr Double Cheeseburger which did not contain those items, but they took it off our allowed list.
I don't do Sonics for $5; I get $15 for the local one. So if I want to change it up (and scrape off the junk) I can go a buck over reimbursement and still come out okay.
Time to build a bigger bridge.