first of all, let me note that I WORK for mcdonalds.
no I do not LIKE it, but...
if you were asked to wait it is because it DOES take about 9 minutes to FRY the crispy chicken for those salads, about 5 or 6  minutes for grilled. it's not ALL done automatically.
stuff DOES run out, ther ARE other people who are before you, there MAY NOT be alot of people working that day.
you DO NOT know what goes on behind the scene.
I've worked days where it's just ME and one other person in the grill area, and let me TELL you, it does get hectic!, all people in their cars have to do is sit and wait, the people inside are busting their butts for your orders.
the food WILL get done, and they DO bring it to you.
I have worked at mcdonalds for a year come august, and I have heard some of the DUMBEST complains.
one time this BIG FAT, ugly arse bull-dog-faced, rooster waddles-down-to-her-knees, obviously-need-a-salad, lady in a MOO-MOO. came in COMPLAINING that there were DEAD leaves on the salad, and I'm in the dining area cleaning tables, laughing to myself thinking "what IS a salad, but a pile of DEAD plant leaves?"
another time, someone complained that the SWEET tea, was TOO SWEET 
, who the heck complains about this stuff????????
usually the teas not sweet ENOUGH, I can atest to that.
a couple other things come to mind, but I can't remember them.
the point is, you had to wait, big deal, next time GO IN to the store, or go back in the kitchen and make your food yourself, see how that flies.
I used to be a complainer about stuff like that, but having worked there, I understand why stuff is like it is.