Rats love toys. Actually, they *need* toys. Not just for playing with, but for chewing on and intellectual stimulation, too. You could go out to the pet store and buy all the toys for your rats that you want. Or..you have tons of toys in your house right now.
Toys include such items as: boxes (cardboard, tissue, wood), chew sticks, balls (ping pong balls will be thrown around), small bird toys that can be hung, rope, paper towel and toilet paper rolls, paper, tissues, paper towels, PVC pipe, and many other things.
Keep in mind that your rat will probably chew the toy to pieces, so you might not want to spend too much money on them. You can buy rawhide dog bones for your rats to gnaw on. Another fun thing for your rat is a hammock. Cut off a section of a pair of pants, put two pieces of string through the inside, and tie it up to the cage. My rats like to sleep inside the hammock, instead of on it. Also, there's the Igloo, in different sizes and colors. The Igloo makes a good nest box.
You can get a running wheel if you like, but it's not absolutely necessary. If you let your rats out often, they'll probably get enough exercise. If you do get a wheel, don't get one with wire rungs. Your rat's feet or tail could get caught between them, and possibly cause a break. The diameter of the wheel should be at least 14".