We tend to use Science Selective rat food combined with a RatRations.com mix. We recommend watching the following video by Isamu Rat Care:
A lot of pet shop treats offer little to no nutrition and often contain added colours and sugar. Choose more natural type treats which will be healthier for your rats. Malt/berry pastes are loved by rats and are very useful for getting them to take medications.
We like to feed our rats peas, carrot, broccoli tops, spinach, kale, apple, banana, blackberries, raspberries, blueberries etc, try to offer them a few different things each day.