I traveled with my mom when she was having her chemo and this is what we did: (This was almost 8 years ago now so just off the top of my head what I can remember)
1) Try to book flights that aren't as full - this may be problematic as you're traveling during the holidays
2) Bring a face mask - so that you don't get sick from someone else. Your immune system is already compromised so you want to reduce your exposure
3) Bring diaper wipes and hand sanitizer - clean everything from the arm rests, to the seat belt including straps and buckles, the tray table, the vent and light buttons, etc.
4) Bring light, easy to digest snacks. Saltine crackers are always a plus.
5) If you need O2 for the flight - this must be booked in advance; each airline has their own rules so check into yours.
6) Have a list of back up flights and schedules - in case of delays or cancellations
7) If possible, have someone travel with you - to help carry your bags, assist you.