Re: Certifications?
If you mean certification in a specialty area (which my hospital does pay extra for), then it sounds like you're not planning to stay in your specialty area (oncology) long enough to pursue this. These certifications require experience in the field and the fee to take the exam discourages "casual" test takers.
Just my suggestion: dig in to your brand new career as an RN. There's much to learn in the specialty area where you are, let alone the other one (perioperative nursing) in which you also have interest.