The sefer Hashavas Aveida k'Halalcha quotes HaRav Eliyashiv shlita as saying that non-Kosher food is not automatically exempt from the obligation to return a lost object. However if there is reason to suspect the person may consume the non-kosher food, it is better to sell the item and return the money. However there are other issues involved. If the lost item can be assumed to belong to a non-Jew, for example it was found in a city that is primarily not Jewish, then there is no obligation to return it. Additionally, if the city is majority non-Jews there is no need to return even a Jew's lost object, because he assumes that it was found by a non-Jew who will not bother trying to return it so he makes it hefker immediately.