I don't know what school KKGisforMe goes to, but at USC we do deliveries & Monday Night Dinner.
I did a quick Google search and it looks like that's not super common at other schools?
What it boils down to is every week, all the members of the PHC and IFC sororities & fraternities have dinner at their respective chapter houses from 5-6pm every Monday night of the semester that there is class. The new members of the house will also go out on deliveries during that time period, delivering gifts from members of their sorority/fraternity to members of another fraternity/sorority. If someone in sorority ABC has something she wants to give to a guy in fraternity XYZ, a group of new mems from ABC will go to XYZ, where they will say, "Hi, I'm [name] from ABC, and I have a delivery for [name]."
Deliveries are often gifts between friends, but can also be a way of thanking your date for attending an invite or formal with you, or, for social/philanthropy chairs, a way to introduce yourself to another house's social/philanthropy chair. At the beginning of the semester, social chairs have been known to send out deliveries addressed to the social chair of a wide variety of frats, as a way to introduce themselves, express interest in having social events with that house, and provide a way for them to contact each other (deliveries usually have a note attached to them). Similarly, if a house has a philanthropy coming up, they can send a note to the philanthropy chairs of other houses reminding them of the fact.
Chapter is usually held after Monday Night Dinner, as the house is already all in one place, and MND is often when fraternities who wish to do so serenade sororities (as was seen in that video of JC Chasez at Delta Delta Delta that went viral a little while back).
KKGisforMe, I've found that cupcakes, cookies, and other baked goods always go over well
I think our social chair has sent out peppermint bark before, because it's pretty easy to make a lot of, if you're sending to a bunch of different houses.