Question: I am a vegan, but a friend offered me some non-vegan food taken home as a gift, which I accepted without knowing its ingredients. How should I handle it? Should I eat it, give it away, throw it away, or return it?
Answer: (The following is advice for all who do not have to survive on random alms food.) If your friend is a non-vegan, and is likely to buy more of that food for himself, herself and/or others, it is best to return it. This is because more of it will be purchased, now that some has been given to you. Not returning it thus has the indirect effect of feeding the supply and demand cycle for production of more such foods.
As you are a vegan, you should do your best to refrain from consuming non-vegan food – even if it is received accidentally, not of your demand. This is because of the reason of supply and demand above, and because subtle greed for non-vegan food might arise, which can subtly urge you to consume more similar foods in future.
Giving the food away to someone else who is a non-vegan is not the best solution too, as it might spur more interest in that food, which again, feeds the supply and demand cycle. Only if the food is not likely to be bought again soon, or at all, should it be thrown away to discourage anyone from wanting more after consuming it – unless the food is absolutely crucial for saving lives in the moment.
Even though discarding non-vegan food seems to be wastage, it is in order to not play a part in getting more sentient beings to develop greed for consuming more sentient beings and their products, that are usually linked to slavery, exploitation, torture and murder. The best long-term solution is to encourage more to go vegan, or at least, to consume less animal products, as they do arise from harm of sentient beings due to market forces of supply and demand. (You can share this article with the non-vegan friend who gave you the gift too, to let him or her understand where you are coming from.)