Tosefta על קידושין 2:1

"Be betrothed to me with this one and with this one [a food item, one-by-one; see Mishnah Kiddushin 2:1]" and she ate the first one, if there remains in her hand something worth a perutah—she is betrothed; but if not, she is not betrothed. "Be betrothed to me with this cup", if there is [enough] in it [the cup] and what is inside it [the contents] worth a perutah—she is betrothed; but if not, she is not betrothed; she takes ownership over it and everything inside it. "With what is in this cup", if there is [enough of] what is inside it worth a perutah—she is betrothed; but if not, she is not betrothed; she takes ownership over only what is inside of it [and not the cup itself].