The supernatant will contain both the DNA and RNA, they won't be very pure (there will still be proteins, salt from the PBS, general cytoplasmic contents). Do you need any protocols for RNA or DNA extraction? We do CTAB-based methods for both (no kit required).

Are proteins found in the supernatant?

Proteins that are amenable to SDS detergent extraction will be in the supernatant, but this is not all proteins, as some are resistant to SDS and will stay in the pellet.

What is in the supernatant after centrifugation?

After an initial centrifugation, the pellet, containing the largest components, is separated from the remaining suspension (known as the supernatant) which contains the smaller components.