A sticky bag zipper can be hard to pull up or down and if it sticks enough the zipper can get broken very easy. Once the zipper breaks you are in real troubles since you probably have to throw out the garment or replace the zipper. Replacing a zipper is not an easy thing to do. You can prevent a zipper from wearing out by giving the zipper lubrication when it seems to be getting sticky and hard to pull up or down on.
You can lubricate a sticky zipper in a variety of ways. The idea is to get the zipper working properly with some sort of sliding material. When you lubricate a zipper make sure you don't get any of the lubricant on the cloth of the garment or it may make a stain that does not wash off.
You can lubricate a bag's zipper with some wax. Close up the zipper and rub an old wax candle or a piece of wax up and down on the closed zipper. You can rub the wax on both sides of the zipper. The open and close the zipper a few times to get the wax to spread on the insides of the zipper. Then the zipper should work much better and slicker.
You can use some soap to revamp a zipper. A bar of soap works well. Just take the bar of soap and rub it on the inside and outside of a closed zipper. Then the zipper should work much better. Soap is a really good way to lubricate a zipper it the cloth around the sipper is washable since the soap will not stain the cloth.
If you are away from home and you have a sticky bag zipper problem you can take some lip balm and rub the zipper. Rub the lip balm up and down on the zipper a few times. Then open and close the zipper a few times to get the lip balm all over the zipper. Lip balm is a great zipper lubricant in a pinch.
Anything that has a zipper may need a lubrication every once in a while. A coat with a zipper or a jacket that has a zipper can benefit from some zipper lubricant. The more you use a zipper the more often you may need to put a lubricant on it. A minute of putting a lubricant on a zipper may save a garment in the long run. :)