That is a good question to ask. What have you done for your parents lately that they did not even ask you to do. They have lives too and we all know they can get stressed out (seriously, my mom is stressing out over her school going onto twitter while I am typing this) and what kinds of things can we do to make their lives a little less stressful in that moment.
For example, I just finished cleaning out our entire refrigerator of all the old food, washed all the shelves and drawers in it, and then washed all the containers that had old food in them.
Just remember, sometimes, its little things, like folding the laundry or taking out the trash, that make the biggest difference for them.