Yes, as a general rule you can store any kind of items, such as cardboard boxes,baby strollers, with no size limit (weight limit of 20Kg applies, please separate your item into smaller pieces if it outweighs 20Kg.)
However, a select amount of shops only accept suitcases and no other type of luggage- please make sure to read the store reservation page carefully to see if your store has set any type of restriction regarding the type of luggage that is able to be stored.