Because they're so quick to assemble and cook, I don't suggest you make the meat or sandwiches ahead of time. That way they can be at their most tender! But for a party, just have all your prep work (ribeye frozen and sliced, rolls cut and vegetables sliced and cooked) done ahead of time. That way all you have to do is cook your meat and toast your buns while you chat with your guests, preferably holding a glass of your fav beverage.