Trying to keep picnic grub from being crushed is always the trickiest part of packing the basket. Luckily, the more this sandwich is pressed, the better it tastes. So go ahead and pile everything on top—the weight from the soda and the brownies will help the vinaigrette soak through the layers of grilled vegetables and cheese, and the crunchy toasted bread will keep the outside from getting soggy.
Game plan: If you have a large grill, you can cook all the vegetables at once to cut down on time. Or make things even simpler by using store-bought roasted peppers.