Tex Mex americana style snack in Chicago

Just before the fireworks at the pier we stopped for a margarita and snack.  We tried to get a second drink to go because we saw a line of people at the carry out window near the bar where we were sitting;  however, they said they couldn’t serve us a to go drink inside – something about a different tab I think. They said we had to go outside to the bar window to order again. What? Stand in line when we just spent $40 in here?  Forget it. We walked along the pier a little and found a much better frozen and heavily spiked margarita!