What is the ruling on paying a monthly sum of money to a shop in exchange for borrowing goods when needed, with the intention of returning the same goods or their equivalent value later?

It is permissible to borrow goods because a loan is valid for any item that is valid for sale. However, it is not permissible to give money in exchange for a loan, as this involves usury, for every loan that draws a benefit is usury.

It is also not permissible to agree to return goods of the same value, because the principle is that a loan is repaid with its equivalent, and because this would be a sale whose validity depends on knowing the substitute at the time of sale. Instead, one can buy the commodity at a deferred price, or barter the commodity for another commodity.