A bird in hand
photo credit: Eric Burton
In English: A bird in hand is worth two in the bush. -- Something that one already has is better than going after something seemingly more worthwhile that one may not be able to get.
Equivalent: One today is worth two tomorrow. -- What you have today is better than what is promised or hope for.
In Spanish: Más vale pájaro en mano que cien volando (same as English)
In Russian: Лучше синица в руках,чем журавль в небе. (same as English)