Well, I think traditionally, the groom's family is responsible for the reception. However, my MIL helped me do some stuff for the wedding. She only had boys and really wanted to be involved.
So I would get with your son and his fiancee and discuss what type of reception they had in mind. I found out that my husband and I had very different expectations than my BIL. We wanted a small reception with finger foods and cake in the back of the church. My BIL wanted a reception at a banquet hall, complete with a DJ, dancing, and alcohol.
If you have a close relationship with the fiancee, you can probably get away with being a lot more involved if that is what you want. I think these days, a lot of the tradition stuff gets thrown out the window.