When I steam vegetables or boil rice I leave it to cool off for a few hours and then put it into a plastic lunch box and then into the fridge. After a day the vegetables get very soggy with a pool of water at the bottom of the lunch box. The rice turns brittle and tastes like sand.  I don't have time to cook everyday, I try to get as much cooking done as possible on Sundays and store the result in the fridge.  I try to Google things about avoiding moisture or drying vegetables but this gives me unrelated results.  Can anyone give me advice for avoiding these problems?  Thank you very much. 
When you approach the low end of the low-and-slow cooking methods, a concern that is normally not an issue in faster cooking methods starts becoming important:  how long will it take the food to get to safe temperature?  You want the food to be above 140 F (60 C) for the entirety of the cooking process, for safety, although having that happen instantly is not possible.  Therefore, you want the temperature to get to that threshold as quickly as reasonably possible, especially for the surface of whole cuts of meats where the greatest risk of pathogens are.  Therefore, I would urge you to err on the side of caution and safety, and use the extra coal at the beginning of cooking until the food reaches at least 140 F.  Once it gets out of the danger zone, and into the safe zone, you have much more freedom.   However, barbecue is far from exact.  I would not worry about a 10 or even 15 F disparity. Your final outcome will likely be indistinguishable.  Still, once the food is safe, if you wish to allow the temperature to be somewhat lower, that is the time to do so. 