No matter what is done, the Teacher should be consulted with.
Because he/she will have the most direct contact with the family and know them.
Then, from there per what the Teacher says... an idea can be born.
And the class/students, partake in it. Even if that is making cards for the family.
Also, the child who's father passed away, will no doubt be going through great emotional hardship and turmoil. Some kids will turn inward and not express anything. Some will be visually in need of comfort. Some may not want attention. Some may need it. So... that has to be considered as well. And I would think, the school Counselor would have insight about the child and how to help him/her. Grief... is a hard thing. I'm an adult, and my Dad passed away after a long illness. For example.
You need to consult with the child's Teacher first.
She/he has to "okay" whatever is done.
But it is of course, very thoughtful to be wanting to do something for the classmate.
Some schools, will set up a fund or collection thing, for the family.... for people to donate to.
In my State, money is often given to help the surviving family/child.
The Father passed away, the breadwinner, and after cancer... so there will be no doubt, a great financial loss as well, for the family. And bills etc.
Then the other thing that needs to be thought of is: if things are collected, how will it be taken to the family??? Meaning, will they want, a whole gaggle of people coming to their doorstep to bring them things or meals daily or what not? Or do they want their privacy and no visitors? So the family, through the Teacher.... can convey, what their wishes are.
And maybe, the family themselves, will have a wish or idea, about what will help or what they need.