A slow cooker is an excellent aid for people who don't have the time or desire to be in the kitchen. Dump your ingredients into your slow cooker in the morning, and you can come home to a hot, home-cooked meal, without the cooking. Many slow cooker covers are made of glass, which can be fragile. Place a hot cover on a cool counter, and the temperature shock can crack and ruin your lid. If you plan to use the cooker again before replacing the lid, you will require some kind of cover to help contain the heat.
Try other lids and pot covers from your cooking supplies to see if any will fit snugly on your slow cooker. A cover needs to help prevent heat and steam from escaping, and should not be so large that it is at risk of sliding off. If you can't find another lid, see if you have a heat-proof plate or serving platter that you can lay over the opening big enough to cover it.
Put your food in your slow cooker and prepare your meal as usual. Cover it with the lid from another vessel or dish that you found to fit over it.
Cut a piece of heavy-duty aluminum foil so that it's a little larger than the width of your slow cooker. Lay the foil over the top and crimp it gently around the sides of your slow cooker for a tighter fit.
Turn on your slow cooker. It's important to crimp the foil around it before turning it on so you don't burn your hands on the hot sides of the slow cooker.
If you can't find a lid or a plate to cover your slow cooker, use a double layer of foil.
Remove the foil and the lid when your food is done using an oven mitt, as they will be very hot.
Clean your slow cooker. If it sat without a lid, chances are it gathered dust and debris while it sat unused. If the basin is removable, clean it with soap and water in the kitchen sink as usual and thoroughly dry it before returning it to the heating unit. If the basin is not removable, use a damp, lightly soaped rag to wipe it down and repeat the wipe down with a rag dipped in clean water. Dry it before plugging it in.