Best Supplements or additives you use

There are a plethora of different supplements and vitamins,oils etc that are beneficial for dog's, what brought this topic up for me was coming across an old post on Apple Cider vinegar and the vast array of benefits it offers canines as well as people. What else is out there that people use? fish oil, vitamin tablets, what do you use and find to be the most beneficial for maintaining and improving your dogs health?
As well if you feed your dogs kibble is there any things you like to add into there food such as egg's, tripe etc? and if so on what type of cycle or how much?
Realistically I would just like to get some insight from those who know what their doing and the benefits from the products they are using, any additional insight whether it be from websites or etc would be greatly appreciated thanks.