GIFTS OF GRATITUDE
May one give a gift to someone who lent him their home or car for the weekend ?
May a borrower give a Bar mitzvah present to the son of the lender?
Case #1: Since ribbis does not apply to items which are not consumed, it would be permitted to purchase a gift for the owner of the home or car.
If the owner asked that utility use be repaid, it nonetheless would be permitted to purchase a gift, as it is obvious that it is being done out of gratitude and not as a repayment for the use of the utilities. According to some opinions the borrower should specify (or include a note) that the gift is out of gratitude for the use of the house. See also “Filling Up the Gas Tank.”—
Case #2: One may benefit the child of a lender if no monetary benefit will be gained by the parent. Therefore he may purchase the gift if the child is over bar/bas mitzvah, and the item is something the parent would not have wanted to buy him. It should also be something that does not benefit the entire family directly. Therefore, a book or toy is permitted (although others may use it, since that is not the direct intention).