I freeze sandwiches made from homemade bread rolls at the weekend, paired in plastic bags, and get a set out at 6 am to take to work in a rucksack. They stay there until I eat them at noon, when they're still pretty cold and wet, possibly because they stay in the rucksack's dark inside. I could make them a bit closer to room temperature by defrosting them in my home's microwave before I leave, or by warming them slightly in a microwave at work, but I'm not sure how much I should use either method or on which setting. Alternatively (if it would be enough, but I think it would be socially suboptimal), I could take the bag out at work so the rolls get some light. Is there an optimum approach?
No matter what you do in this situation, you are likely to end up with soggy sandwiches. This has nothing to do with light. Firstly, the bread of pre-made sandwiches will naturally pick up moisture from the filling and condiments. Often, even freshly made sandwiches will become a bit soggy by lunchtime. You've also created a further disadvantage by freezing. Freezing and thawing disrupts the cell structure of foods. When this happens, moisture is often lost. Of course, the bread will absorb this moisture. A microwave will thaw and warm, but will not remove much of this moisture. You would have better luck with an oven, but that would be more time consuming. Really, your optimal approach is to prepare the ingredients in advance, then take 2-3 minutes before you leave for work, and make a sandwich.
I think it is worth looking at your sandwich making process to see if there are any things you can do to reduce the likelihood of this dampness.
You mentioned that you freshly bake the rolls, do you allow them plenty of time to finish cooling and releasing steam before you start making them into sandwiches?
How 'damp' are the meats you use for fillings? Some processed meats have quite a high water content. Could you experiment with cheese or with drier meats like salamis or dried ham instead?
Does you mayonnaise have water listed as an ingredient? Many of the lower calorie mayonnaises have that and it can make the bread damp if it is in prolonged contact. A water-free mayo would avoid that, as would butter. Or can you keep a jar of mayo at work and add that just before you eat your sandwich?
You also say that you wrap them in plastic, which will seal in any moisture that might otherwise evaporate. You could consider a couple of options to combat that. You could unwrap them from the plastic in the morning and place them in a paper bag, or have them wrapped in paper kitchen towel inside the plastic as that wuld absorb some of the free moisture.