When you commute how do you carry your lunch? Or do you?

When I start commuting both ways to & from work, 28 mile round trip I will need a way to keep my lunch cold. At work we have refrigerators & microwaves to use. It can & does get warm & humid even in the morning in my area in the spring & summer. I will probably not want to take sandwhiches made with cheese or mayo or meat for fear that it will get too warm & cause me to become sick. I can find a good selection of healthy frozen microwave meals to eat. Because they are pre-cooked would they be a good choice? The only way I have to carry my lunch is in my saddle bags.

The cleaning crew cleans out the refrigerator/freezers once a week & throws away what ever is in them. And people have been known to steal another person's frozen meal. Otherwise I would consider stocking up with a weeks supply of lunches.

How do you do it? What do you suggest?