I have always kept "set boxes" especially those with artful box tops or lids. However, I agree with the comment on Marx boxes, they are sturdy for sure but for a number of years the box lids were pretty common and plain. If I am going to display a car and I have its component box, I tend to "collapse" the box (sometimes I have to handle the inner sleeve separately or sometimes it goes to trash (Horrors!") and store it flat.that way I have the box should I ever want to sell or trade the car but it takes up less space. Now after almost 50 years of trains, knowing what boxes I have...that is a different story
Don