I guess that really depends on why you bought your cards in the first place as for how you should store them going forward. If you bought them to use, to evoke memories, view them and display them then a business card holder is a great choice. Stick them on your wall. A little Blu-tac on the back and you can put them on the wall., in fact just about anywhere.
I like to look at my cards often so I have them stored multiple ways, in a couple of name card boxes (so I can go through them any time). Others in business card holders as well as a couple of full sets I have tucked away for safe keeping in an envelope.
They arrive in a sealed but not watertight bag so if you don’t open the pack they can be safely stored anywhere out of water really, just leave them in their pack, lay them flat somewhere, they will be fine.