Toasting sandwich bread before packing a lunch - when is it appropriate?
I usually toast most of my sandwiches (or the grilled cheese kind) for hikes and picnics. My general rules are: no filling that releases water (fresh tomato, for example) and wrap in paper (tissue or napkin) and then plastic or foil (or a cooler/plastic container). Keep in the fridge until needed or when packing your bag. The paper will prevent most of the moisture from condensation making your bread mushy. It won't have the crispness of fresh made toast, but it's pretty good.