As to the expensive PLB solutions recommended, I suspect few will go such an expensive/high maintenance route.
However, I do see an advantage of having a beacon in late evening sessions or fog, even if you are in a group. If you are detached from your kite, it is very difficult to spot you. Something small and cheap like the link below will likely be purchased, worn and therefore available in the rare emergency event. So I am thinking about getting a few of the following:
http://www.amazon.com/C-Light-Safety-Li ... 409&sr=1-2