The Pickled Shallots can be made up to a week ahead. To transport, pack the filling in a plastic resealable bag and pack the whites separately in a sturdy container, then place both in a cooler with ice. Pack the toppings separately, they do not require refrigeration. When ready to fill, snip off a corner of the resealable bag and pipe into the whites. Keep some filled halves in the sturdy container in the cooler until ready serve. Finish with the toppings and serve.