Firstly,

to you for being such a caring friend!
I have been battling cancer for a few years now - Stage 4 metastatic - just finished another 10 rounds of chemo. The nicest things anyone's given me have been prayers & cards with heartfelt wishes, but I have received some very nice items that have been a help. Here are some suggestions:
Comfort items are much appreciated: chemo & radiation cause dry skin, so body butters, lip balm will be appreciated. Head wraps, soft robe, aromatherapy wraps, cozy socks, slippers, etc. A journal to write down feelings. Hard candy to help with dry mouth & sores. A funny mug with a variety of teas (be careful of herbal teas - herbs can react with meds) or hot cocoa.
NOTE: Just be sure to check to see if there are any allergies/reactions to medications. Also, some cancer patients experience a change in tastes & smells so some scents/flavors, while nice normally, can be difficult for the patient.
Also, anything that takes the mind off the cancer for awhile is welcome indeed.
Laughter is great medicine - I have loved getting funny movies, cards, books, etc. Sometimes the patient just gets tired of talking/thinking about their disease.
As for inspirational books, a couple I can recommend are:
- There's No Place Like Hope: A Guide to Beating Cancer in Mind-sized Bites
- Stronger Than Cancer Book by Connie Payton
I hope this helps. I'll pray that your friend recovers fully.