Good toys for cages can usually be found around the home. Empty boxes, the cardboard tubes from toilet paper or paper towel rolls, hanging rope to climb on, etc all make good mice toys. Also, do not forget the water bottle. You will need to either buy a food mix or lab blocks balanced for rats or balanced for mice. You can also make your own mixes if you are careful to balance it for your pets nutritional needs.
Rodents can and do get sick or injured.
If they do, it is your responsibility to properly care for them and this usually means seeing a vet. If your animal broke a bone, was seriously injured, needs tumour removal etc and needs to be operated on or Xray'd expect to spend much more money. Unexpected medical emergencies, and colds are all unfortunate but common aspects of pet ownership. Mites sometimes come in via wood shavings and require treatment. Fleas are not very common fortunatly, because unlike cats or dogs your rats do not go outside.