Simply replace the unfilled areas such as "" and "[date]" with your information.
Dear [name of rep at vendor],
Thank you very much for the [list gift(s)]. I very much appreciate the thoughtful gesture.
However, due to company policy, I am not allowed to accept this type of gift from a vendor or supplier. This type of gift can be considered a bribe, despite its obviously innocent intent. I am therefore returning the gift to you. If you would like to provide us with a token of appreciation in the future, we would like to suggest that you make a donation to the charity of your choice and let us know. We are a company that truly believes in giving back to the community.
Thank you again for thinking of us. We have always been very satisfied with your services and products, and we look forward to doing business with you.