Lovemyson101,
Others have already covered most of what I would have told you about rehab visits.
The somewhat local (1+ hour drive) where my daughter went had some rules which were somewhat strange -- the oddest was that there was no sugar or caffeine present on site. Therefore, no soda, "real" coffee or tea. I guess substance free is substance free although they permitted smoking in designated outdoor areas.
When we first visited her she asked for Sugar Free Jolly Ranchers. As others have said, everything and everybody was subject to search and any items brought in were inspected by staff before they were given to the patient.
This rehab had something which they called "Family Wellness Weekend" which was a three day weekend marathon of large group and family counseling and addiction education. We all learned a lot about ourselves and each other during that weekend, I have and still do describe that experience as "learning to cry with strangers". That being said, I would not miss that experience for anything.
At the end of the weekend they presented everyone with an inspirational medallion - mine has a very peaceful scene on one side which is a view of a lake or bay and the Serenity Prayer on the other - it is my "magic object" (my other word with the same meaning was "censored")t******n and has always been in my pocket since that day.
Visit your son and just accept him for where he is at the moment.
Keep coming back,
Jim