Is it safe to take amoxicillin/clavulanate that is expired?

No, its probably not as strong as it should be. Also if you have it just laying around, its because you didn't take all of them when the dr put you on them. This should never happen, because they order the amount you need for a full course. You will again not be able to take a full course. See also, this article on drug expiration dates.