It would be a good start to be able to search for multiple items in the store using keywords.
The old client (RIP, oh thy bugged, but still better spaghetti coded thing) worked with keywords, such as "veigar+yi", and you'd get listed all skins including those letters in that order.
In the useless new spaghetti coded POS of a thing, you MUST use the full name, for example "Super Galaxy Nidalee|Super Galaxy Elise".
But saving searches as a "shopping cart" sure would be an interesting feature. Then the system could send notifications whenever content in that cart would either be available (if legacy content) or on sale.