I have never been to a Catholic Mass yet. As a "searching" baptist the baptist church has a lot of opportunities for fellowship. Are the Catholic church members close nit as in do they fellowship with each other or do they just somberly go to mass and then go home?
Well, it's a different kind of fellowship. There aren't Sunday school classes and church potlucks and whatnot; but (depending on the size of the parish, I would guess--I've only been back in the Church for a short time, and so only a member of one large parish) most of the fellowship seems to be centered around ministries.
Fellowship takes place right after Mass in the hall for coffee and donuts!
Except for tiny tiny parishes, all in the US have "Sunday School". It is called RE, CCD, PRE, Faith Formation - many different names, all of it is classes that are divided up by age.
Potlucks and picnics? Yep, those are very big in the South. They also go by the name "festival" or "bazaar".
Read the Church bulletin, you will be surprised what all is happening, read your Diocese web site for happenings at other parishes, look at their bulletins and websites.
But for many non-Catholic Christians, Sunday school is different from what I've seen with RE, CCD, et al. Sunday school classes often have officers, and they check roll, and have newsletters, and visit newcomers, and have baby showers and holiday parties, and sometimes additional weekly Bible studies, and more. It is your small group within the larger body. My experience (so far) is that people show up for the Re, CCD, etc., do their thing, and go home. It's all quite friendly, you know, but it isn't (or hasn't for me) building relationships outside of the church.