Because you're going to a peds hem-onc unit, a huge part of your day will be working with central venous lines. So you could put down dressing changes, cap changes, blood draws (if your hospital allows students to draw blood from CVLs), flushing, initiating and discontinuing infusions and accessing implanted ports.
Children on chemotherapy often have problems with their oral intake; they may require placement of either a nasogastric or nasojejeunal feeding tube. Add that to your list.
Your patients may undergo bone marrow aspiration or lumbar puncture. Assisting with those will be part of the job. Put those on your list.
Skin and oral care are very important for anyone with cancer. You may be able to come up with a related skill you could hone.
Administration of blood products is another huge common feature. Add those to your list.
If I think of anything else I'll be back.