I always kept their rat seed in a bowl inside the cage, but I also daily gave them things like : yogurt, cheese, pretzels, pizza crust, cooked spaghetti... just anything I cooked, we would share with the rats. They lived about 4 years.
I always kept vitamin drops in the water bottle too. Just visit your rat daily, put it on your shoulder and walk around.. feed her snacks daily by hand.. Rats are generally very friendly... if you pick one at the pet shop, get one that comes right to your hand, and seems eager to meet you. Once used to you, and the surroundings, your rat will be so happy to see you.. will want out of the cage when you walk by.. They are really smart. My daughter let hers out every evening while in her room doing homework, or watching TV... the rat was out for like an hour each evening, which they really love..
Remember, rats at some point will need to see the vet.. they are prone to pneumonia ( labored breathing, and laying in the same spot all day ) Don't let it go too long, it is a horrible death.. find a vet who sees rats. And if they don't chew on enough things, their teeth actually grow and grow, and will need to be clipped. I found this out one day, one of our rats teeth had grown up into her sinus cavity.. I just one day noticed she had blood in her nose.. took a closer look, and saw that she couldn't properly open her mouth because her teeth grew upwards soo much. They also get cancer.. not much you can do about it though.. You should have a few good healthy years with your pet rat.
If you can, try and buy a 2 or 3 story cage with ramps to run up and down the levels. Its just more room, more fun for the rat.