I used to raise rats (for many years) & bought quality name-brand lab pellets for their basic diet. (Not all brands are available in all areas.) No junk food ever!
I also supplemented with many other things: they enjoy small bits of raw fruits & veggies (focus on nutrient dense options like kale & carrots) & giving treats
of seeds, nuts, peanut butter, hard cooked egg, popcorn & table scraps* will keep them healthy & friendly so you can handle them easily. *avoid spicy/hot/salty
(if you consume peanut butter, your rats will do a GREAT job of licking it clean when you're done with the jar & they also love to gnaw on cooked bones- they're
good for them- for minerals etc- and safe to give to rats, unlike dogs.)(they'll lick out a cottage cheese container too but don't leave it for long as they eat the
plastic too)
You don't have to give anything else besides fresh water & quality lab pellets (balanced for rats) but they enjoy SO many other things, if you're anything like me,
a day never went by that I didn't have some extras that they benefited from.