I often save the liquid left over from a whole roasted chicken (or turkey). I typically place the liquid in a mason jar and store it in the fridge over night. The fat will rise to the top and the rest of the stock will settle to the bottom. Scrape off and discard the obvious layer of fat from the top but keep the bottom layer. The stock can be used as the base for cooking again later, like for sauces (like a peanut sauce) or for gravy or some past sauces too. I often freeze it so I can use it later on.
The photo shows the fat on top that can be discarded and then the stock that can be placed in the freezer for later.
Stock like this will be gelled because collagen from the bones is extracted during the cooking and remains in the liquid. It makes for a richer stock though so don't be alarmed. Instead, appreciate!
Apparently, if you keep the fat on there, it can stay in the fridge longer. Not sure how long though... you'll have to google that.