Tickets will be issued on a first come first served basis.购票按顺序，先到先得。The campsites are first come, first served, so we'd better get there early. = The campsites are assigned on a first-come-first-serve basis, so we'd better get there early.露营帐篷搭建地是先到先得，所以我们最好早点到那儿。