I've been to one in the past when it was held in Norfolk. The Saturday included guided visits to Holkham and Houghton, both of which were absolutely fascinating. There was a dinner on the Saturday evening, which I enjoyed, and then the AGM on the Sunday. A lot of the AGM covers the formal proceedings necessary each year (passing of the financials, election of Committee, etc) but there was some interesting discussions as well.
Remember that BDS is a charity concerned with deer welfare, not a stalking organisation (though there are of course lots of members who are stalkers). So if you think you'd enjoy a weekend talking about all sorts of things deer-related to all sorts of people from all sorts of background, give it a go.