I haven't tried a McDonald's drive thru, but my local Burger King and Del Tacos haven't had a problem with me using their drive thrus. I'm usually buying it to take home, so I don't buy a drink. I use the Topeak trunk bag with fold out panniers. After I get my bag of food I'll ride to the end of the drive thru with the bag in one hand, park in a safe place, unfold one of the panniers, and place the bag inside for the ride home. I find the drive thru much more convenient than locking up and going inside. I usually don't carry a lock with me anyways since I can park inside at work, and anywhere I stop on the way I either go through the drive thru or bring my bike inside with me.