Well, RattiesSix pretty much covered it. I'll still make a list of things I use/have though. Never a such thing as too much info
And of course you don't have to use the exact same brands or all this stuff.
Food bowl. I like the kind that attach to the side of the cage
Oxbow Regal Rat Food
Dry Mix for added nutrients and variety (I buy mine from Shawna Laufer but there are other very good people to order from as well. Or you can make your own)
Fresh Fruits and Veggies such as carrots, broccolli, squash, spinach, blueberries, strawberries, melon, apples, bananas, etc
Treats. My rats love yogurt drops and also this Gerber Graduates puff cereal snack. It's healthy and they go crazy for them!
Yogurt and soft baby food
Multiple standard hammocks
Hanging beds, tubes, honeycomb hammocks
Igloo or other hidey house
Cat toys (NO catnip though!)
Hanging hooks for toys
A wheel-I do not have one anymore, but I do recommend one
The Dollar Store has GREAT plastic baskets and dog/cat toys!
I use liners made of fleece
ExquisiCat Unscented Paper Pellets for litterbox
Fleece scraps for nesting
newspaper or towels for under the liners
Unscented baby wipes for spot cleaning the cage daily
For weekly cleans I use this pet/baby safe natural spray cleaner. But a vinegar mix will suffice
Scent free detergent for washing any fabric toys
Money for a vet incase they get ill
Bonding pouch. This isn't necessary. In fact I personally, do not own one but a lot of people swear by them
A carrier for vet appoitments
An extra small temp. cage-you never when you'll need one!
Okay, I'm probably missing something major here, but I did this all off the top of my head