As far as the Chemo, the major side effect that I had was slight ringing in the ears. Also, I felt a little off the 3rd and 4th day after each infusion. I didn't want to say "queasy", because it wasn't quite exactly that bad. I was infused with 2 anti nausea drugs during each infusion, and also had Zofran pills to take on demand, but I only needed them twice, and I never vomited. So I can't complain too much there.
The other issue, was my veins being sore from being poked so much, so try not to let them put the catheter in the same area all the time. Especially if he needs infusion hydration for a week or two after the treatments. They let me keep the catheter in for a few days if I was getting consecutive hydration infusions.
Now, the radiation was a breeze at first. Don't be fooled, it takes multiple visits to kick in, but I see the side effect time line varies greatly when I read though the forums.
Throat mucus will develop which will cause sleep problems, and coughing, and just makes everything orally more difficult, like brushing and gargling. His neck will get sore from the skin being kind of burned like a bad sunburn, they may give you a skin cream, or you can purchase OTC aquafor. Just don't apply it for 4 hours before radiation, it's basically Vaseline, and I guess gets too hot during the radiation. Most people apply it immediately after each treatment. And the worst of the side effects, eating issues due to loss of taste, and throat pain. So it's good to know it's normal, and will be an issue during and well after treatments. Having a feeding tube, is a very complex discussion that I won't get into. I just managed to get by without one, but it was very close, my weight dropped very steadily the last few weeks, and up to a few weeks later.
I managed to just avoid it by getting hydration until I was able to swallow fluids without major pain.
Don't be scared by this, knowledge is good.
I was able to handle the side effects so much better because of the wealth of experience our fellow forum members provided here.

Enlarged left cervical lymph node in neck on 1/9/18. Male, age 60. Had retired from working as a computer technician and a project manager for almost 38 years, on 7/1/17.
Node was removed 1/16/18 and found to have SCC P16.
Chest xray clean.
Since then, PET/CT, slight activity left parotid, possible malignancy left lingual tonsil. MRI clean.
3 endoscopies, nothing seen.
2/26/18 Larryngoscopy,primary not found.
TORS 3/23/18 lingual tonsil biopsy.,biopsy negative.
Chemo/rads started 4/18/18.