Everyone is going to have a different suggestion because everyone is different and has different preferences. My mom passed away 3 weeks ago and we live in a different state than she did. We had a lot of travelling to do back and forth in the weeks before and after her death. A dear friend had some meals ready for us when we arrived back into town along with some staples like milk, and eggs. It was so appreciated!
We also got a plant that is pretty and my DD likes watering it, taking care of it in her grandmother's memory.
Life goes on very quickly for everyone surrounding the family, but the hole in their hearts is left behind, (you are so busy during that time but it's like a holiday letdown when all the busy-ness is done) so to do something after the fact is appreciated.
OP, sorry for the loss of your friend's dad...