slightly related to this question: according to the tradition that one should not take food from a Shiva home to eat elsewhere outside the home; does this include taking food after the shiva period has ended (ie leftovers)?
It's tough to prove something is prohibited if there's nothing specific that indicates that rule. However, I'm citing from this article that says:
There are Poskim who opine that nothing, whether objects or food, should be taken out of the place of mourning during the entire Shivah, as a Ruach Raah (unfavourable spiritual influence) rest on the abode (Eliahu Rabah 224,7. Lechem Haponim 376). Some rule that the restriction applies only if the death happened in that home otherwise it in not relevant (Chidushei Rabbi Akiva Eiger 37). Other authorities state that this tradition has no Halachick basis at all. (Yosef Ometz p.330), Nitey Gabriel 92,1 writes that this seems to be the accepted custom. When the prohibition of B’al Taschis (discarding good usable food) is also involved, this last one would have priority.
I've bolded the critical phrase, here. It seems that the custom exists only during the shiva period, and the author has cited Eliahu Rabbah for the source of that minhag. So, it seems that once the shiva is over, the Ruach Ra'ah is no longer present.
Even during the shiva week, depending on the amount of food and when it was brought, there may be a good chance that these left-overs would be disposed of, anyway. In such a case, you would be doing a mitzvah if you took it and ate it yourself or gave it to someone else, esp. a needy hungry person. However, as the mourners themselves should not be occupied with anything other than the mourning, I think it's improper to ask them, directly. Usually, a non-mourning relative or someone else is in charge, and proper etiquette seems not to ask at all, but if someone hints to you to take the leftovers esp. if they mention that it will be disposed, I can't see a reason to refuse the offer.