I've organized a few gatherings around the Traveling Portfolio (which seems to have gotten stuck in the doldrums, since I haven't had time to manage it, and no one else has stepped forward to take it over), and usually what I'd do was suggest a few possible dates for a get together with the local portfolio participants and any other interested members within easy traveling distance, and we've met up at my place or the home of another participant, maybe with wine, cheese and appetizers. People have often come with portfolios of their own in addition to viewing the APUG Traveling Portfolio. I usually put out several pairs of cotton gloves, so we can pass prints around.
One time there was a free B&W workshop at a nearby National Wildlife Reserve, so we decided to attend as a group and look at the portfolio afterward.
I've been to a few LF outings in the NYC area as well. For gatherings in easily accessible locations like Central Park, we've just started a discussion and come to a concensus on a time and meeting spot (maybe adding an additional meeting spot and time with shared cellphone numbers for latecomers), and met there. For places that require driving, part of the organization is figuring out who can drive and who needs a ride (since many New Yorkers don't own a car, even if they know how to drive and have a license).