To make boxed cookies moist, you can try a few different things. One option is to add an extra egg to the mix, which will increase the moisture content, but be aware that this will make your cookies spread more than usual. You can also try adding a tablespoon of sour cream or cream cheese to the mix, or a teaspoon of honey or molasses. Another option is to underbake the cookies slightly, which will keep them moist and chewy.