What should I expect after the barium enema procedure?

Lots of barium. Barium will act as a laxative. Stay near a toilet.
Mostly gas. If you had a double contrast study then the gas that was introduced into the colon and small bowel will make its' way out the usual way. You will also notice that you will continue to pass barium (white stuff) for a while. Since your bowel was well cleaned out before the exam (i hope) it will be several days before your stools regain their typical appearance. There may be some cramping.