The first is the goblin story, which was very much like A Christmas Carol. Well except about a poor sexton rather than a rich man and the ending is a little strangers.
The second - Mr. Pickwick goes skating but not before he berates Mr. Winkle for being a fraud. Once again Mr. Winkle has pretended to be able to do something he can't. Before this takes place we meet a couple of medical students. I think Dickens may have thought less of medical students than he did lawyers which is saying something.
The third - After he and all of his friends are served with subpoenas, Mr. Pickwick visits his lawyers and we meet the lead lawyer in the case who promptly shuttles everything to the junior lawyer.
All in all, keeping the story moving. Some of the installments seem a little strange to me since I would have thought they'd be a little more cohesive but that's not always the case.