Suppose we take Thanksgiving in America, then on the day of it, eating a turkey is expected and seen as a highly meaningful activity. However, eating it the day after, or a week after or a month after, seems to hold much less meaning than on the day of thanksgiving.
If the meaning were due to a social event or periodicity, then it could've been shifted away a few days or done without context.
Then, what is it in culture that makes it more meaningful to do it on the day of thanksgiving?
I think this question has things reversed a bit. Culture doesn't 'add meaning' to acts (as though we were going to do those acts anyway). Culture defines acts as meaningful, by creating a set of ritualized behaviors where acts are connected in specific ways. Thanksgiving isn't just chowing down on turkey; thanksgiving is a day of rest, a gathering of far flung family, a particularly earthy kind of meal with particular menu choices, a remembrance of difficult times and a celebration of bounty. Culture recognizes and defines a moment as special, and defines what rituals occur on that special moment. We might do the same things on other days, but they are not ritualized as they are on that special day, and thus don't carry the same meaning.
I'm not following your second sentence, and "meaning" can be a notoriously vague and vexed term. Let's just say that any and all acts, objects, gestures, words, can be rendered "symbolic" or "representational" by context and association.
A urinal is simply a urinal, until Duchamp places it in an art gallery. In this surprising context it acquires more complex associations and invites questions about both itself and this new context. A cross may be a crude wooden instrument of execution. But by association with a specific life, death, and ressurection any cross may henceforth acquire an imponderably vast freight of associated ideas and hopes.
Similarly, eating turkey per se means eating what happens to be turkey. Eating turkey in the commemorative context is representational of much besides turkey and eating, as Ted Wrigley notes. Nothing in culture is entirely free of association, of course, but many things are arbitrarily "stickier" or more symbolic than others.
We might also refer to "meaning" in the manner of Luhmann as a kind of sliding ratio between actual and possible. Certain acts or "actuations" open up more possibilities than they foreclose. The "possibilities" here are the network of associations summed up by this contextualization of the act of turkey eating.
But I'm not sure if this is what you are getting at, as I say, the second sentence isn't clear to me and a complete answer would really end up being a definition of "meaning," which is pretty hard going.
