What can i give my 13 year old yorkie for a cough until he goes to the vet?

Coughing is Helpful: Coughing was "invented" for a purpose: to bring up mucus, clear the lungs of unwanted material. If you "treat" the cough, and try to suppress it, whatever is intended to be coughed up has a greater chance of sticking around, and causing further problems. Yes, this is a dog, but the advice is generalizable for humans. The dog is unlikely to have to get up in the morning, so no cough meds needed.