While some cats will be OK if left alone for short periods of time while you're away for a night or two, it's not recommended.
Even if you leave enough food and water for your cat to consume while you're gone, what happens if the water bowl tips over, or if the cat runs out of food? If left alone for too long, the cat could suffer medical complications if he or she goes without food and water.
If you're leaving your cat alone for a night or so, there are some food and water dispensers that will give your cat food and water periodically and protect it so it doesn't spill.
It's still a good idea to have someone check in on your cat at least once a day while you're away.