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。

“Aren't there any cookies left?” “Sorry—first come, first served.”“还有饼干吗？”“对不起，已经没了，先来先得。”