Cry and Grieve for as long as you need to. Talk to people about it. There are also Bereavement Groups that you can talk to if you need to.
Do something nice in his honor. What did he enjoy?
We started a library for the local Ronald McDonald House. Perhaps you could collect games for the children's ward at a hospital near you.
Let yourself have time to grieve. Sometimes it takes longer to grive and go through the process. It is ok to grieve and be sad over his death.