Haven't really had to worry about it as we've always stayed together well. If we do split up then there is the usual we'll meet you at.....and have never had a problem with it. That's not to say that we ignore the potential problem. Going to many airshows and things of that size, we usually have a brief 'briefing' before it. There is the usual stop and take a moment to look around you. We may be only a few steps away. If you realize that you can't find us then find 1.Police/Medic/FD or 2. {one of a kind prominent landmark}.

fortunately, we haven't had to use it yet. That said (and now that I've jinxed myself) I'll let you know how the plan works when someone gets separated next weekend.