How to Meal Prep Steak and Potatoes for the Gym

I am a big fan of the classic steak and potatoes meal but I have never tried to meal prep it before. I am worried that the steak will get tough and the potatoes will get dry when I reheat them in the microwave at the gym.

I am looking for tips on how to cook steak for meal prep. Should I undercook it slightly on Sunday so it finishes cooking when I reheat it? I am also wondering what the best type of potato is for staying moist. I have been using Russets but maybe red potatoes are better.

Does anyone have a favorite marinade or seasoning for a steak meal prep? I am in the US and I usually buy my meat at Costco. I want to have a solid high calorie meal ready for after my heavy leg days. Any advice would be greatly appreciated!