Amy,
I don't know if your dad should be drinking beer, I suspect it doesn't make a big difference before starting radiation. But missing a doctor's appointment to do so seems more important.
I had surgery and my mouth started to heal before I was told I needed radiation. I refused a feeding tube at the start, thinking however bad the radiation would be, I'd rather tough it out than have a tube. Turned out I needed to have the tube installed after about 41/2 weeks of radiation which was much more painful and unpleasant than doing it beforehand would have been.
The side effects of radiation make the mouth so sore and inhibit the ability to swallow that a feeding tube can make a huge difference in being able to stay well hydrated and fed. As many on the forum have indicated, it is not really a big deal and it makes things so much easier when the radiation side effects really build up.
Perhaps your Dad could post directly to this forum and hear first-hand from those of us who've had a peg and appreciated how useful it turned out to me.
One of the more unpleasant side effects of radiation is the thick mucous that it creates. Taking Robitussin via the feeding tube (don't take it orally) had help to thin the mucous and make it easier to cough up.
Best wishes and good luck with your dad's treatments. - Sheldon