zipper of coat not closing

When the zipper of your coat is not closing you can try to make it work by running a candle over the zipper. It should make opening and closing a smoother activity.

When you can't make it work, and you've got no bottons to make it work, put an old cardigan over the coat.

Wear on your body an opened paper that covers the front of your upper body.
The paper is a good and very old fashioned isolation.

The cardigan should keep your coat closed. You can also try tape to close your coat. Especially sparadrap/hechtpleister/leukoplast works great, but be careful, the adhesive leaves spots which are not easy to remove.