I had a friend who's husband went through chemo...the thing she always asked for was food that she just had to pop in the oven. The thing is though, her husband had special dieting concersns/issues that changed throughout the treatment. One time she asked for high fat/high carb food, like super cheesey mac and cheese. Another time he wasn't really hungry but needed all the nutrition he could get, so something like low fat, loaded-with-high-power-veggies-and-whole-grains soup was on the menu.
Also, if there are kids involved, age appropriate snacks were also requested - like cereal "cookies" they could grab on the go for breakfast.
Also, whenever I dropped food off, I asked if there was anything they needed from the store...Usully she said no, but sometimes an order of fresh fruit or for a big pack of tp was placed.
If you're not into cooking, but have some time, general offers of running errands would probably be appreciated. Anything to save the family time would be great.