Hi talkingnonsense, - sorry to hear your dad is poorly, I hope his treatment goes well. I had chemo for breast cancer a few years ago, so hopefully have a few tips for you 
Yes you are right about the constipation - steroids (which they give you for several days after chemo) bung you up, he'll be advised on taking laxatives if necessary - movicol works well - (he can get some form the hospital or GP) better than things like senna which can be a bit violent! Prunes, prune juice, dried apricots - all good.
so plenty of drinks - he'll need to keep up his fluid for the first 24 hours anyway to help the chemo flush through his system. I found fizzy drinks most palatable (even though I don't normally drink them)
Later in the cycle - he might find it goes the other way and he gets diarrhoea - again fluid very important, and ask the unit/gp for tablets otherwise you can get dehydrated.
He'll need a thermometer - very important to keep an eye on temp. and contact his unit straight away if it goes up. Chemo makes you more likely to get infections which you can't fight properly without help.
Peppermint, ginger and lemon tea all good for sickness - they work best if you alternate them and don't stick to one flavour all the time.
There are lots of possible side effects that he may or may not get - everyone is different. My main tip would be to make sure he uses his team to the full - there is something to help with most side effects, he only needs to ask, don't put up with anything you don't have to. (I say this because I know some older people think they are being a bother if they ask for things). especially the sickness - there are lots of anti-sickness drugs, - if one doesn't work ask for a different one. Sickness isn't inevitable though - some people aren't too badly affected.
I listened to a lot of audiobooks - nice when you are too tired to read or watch TV, also nice to listen to while you are having your chemo - it takes a couple of hours to got through so can be a bit boring, - has he got an MP3 player or something he could have music/books on?
Skin can get very dry and sort of papery - so moisturizer is good, I used a baby one (olivio I think it was from boots), also a child's toothbrush is good as your mouth and gums get a bit delicate so you need something gentle. (he should be given a mouthwash to use to help keep ulcers at bay, - he needs to use it frequently, and if he has any problems in that area, again tell his team so they can give him something)
I expect this all seems a bit overwhelming, - there are lots of things that can help - and I'm sure others will be along with loads of suggestions. Just shout out of you think there's any specific questions I might be able to help with.
Loads of good wishes to your Dad