There’s this store that, for the past few months, has been giving customers a gift voucher when they make a purchase. The voucher lets you get a random item from the store for free. You can get a maximum of one free item per week after making a purchase over 1€. Would this count as gambling?

It depends on why you are buying. If you want the item itself and would buy it anyway at that price, the voucher is a gift from the shop and there is no harm in it. If you are buying in order to get the free item, or the shop has raised its prices to cover it, then you are paying for something you may or may not get, and that is gambling.