I see a lot of friendly meant comments, but please note if the guy is getting chemo his taste and mouthfeel can completely change. In other words, greasy foods like stews simply won't go down and if you manage to eat it, it's extremely difficult to keep it down. If he will be using irinotecan you might want to completely stick with what the doctor advises, as high calorie diets can trigger some serious side effects. Unfortunately foods are quite limited when you'll get chemo, stuff what you liked all your life can suddenly taste horrible.
A quite healthy and easy to digest food for people with chemo is zupa pomidorowa (polish potatoe/tomatoe soup). Very cheap to make, not too fatty and contains everything someone needs. It has some meat (beef or chicken is best), potatoe, rice or noodles (whatever you prefer) and obviously tomatoes and soup veggies. Don't make it too salty, that usually doesn't go down well. He can always add some when it's to plain. It freezes well too.
Other stuff that goes down well is chicken rice, steamed chicken (you can buy cheap oven bags these days), soups. I forgot how it was called, but there's also a lentil based dish indian people make for sick people (not really spiced) which is very good as well.
Don't put stuff in the fridge for 4-5 days. A normal person wouldn't get sick from it, but chemo ruins your whole immune system as well. Just freeze it in containers from your local takeaway. I'm pretty sure they will give or either sell you a bunch of microwave ready containers if you tell them your motivations. Than you're also not stuck with cleaning those out everytime, just throw them away after he's done. If he's on his own, he can even eat from the container to limit the work for him. Pack it in smaller portions, it's easier to reheat and especially in the first couple of days he won't be finishing large plates. It would be a waste if you made a lot of good food just to throw it away. If you freeze it you don't have that problem.
Edit:
By the way, I admire your support. Unfortunately that's not something you can take for granted these days, thanks for that. I can also recommend joining a cancer forum, as there's a
lot around cancer and the treatments you will need to understand. The psychological part is really important as keeping someone motivated to fight is the hardest part, even if that person becomes an annoying, cranky, angry ******* after a while. There are complete networks that offer voluntary support to patients with less of a social environment. Cancer affects a lot of people, so there are plenty of highly motivated people willing to help out where needed. Those people can also support
you in though times.
I wish you both the best for the coming months. With pride I can say though, survival chances increased significantly over the last decade - so the odds are in your favor!
Please also consider participating in the GEL (Genomics England) project. It does not help you directly, but it will make a difference for our future generations.
https://www.genomicsengland.co.uk/taking-part/