"It's such a chance! You shouldn't miss it!"
Here, I have something special for you! We have special word for "a lucky chance," - in contrast to something random, something that makes you shrug your shoulders, - it is something that makes you happy, makes you feel lucky, - an opportunity, in other words!
And this word is - הִזְדַּמְּנוּת
So, the sentence above - "it's such a chance! don't miss it!" would be
זֹאת כָּזֹאת הִזְדַּמְּנוּת! אַל תְּפַסְפֵס אוֹתָהּ!
If you happen to buy something cheap, or just something convenient and on your way, you tell your friends - if I translate loosely - "Look, what I happened to buy!" - !תִּרְאוּ מָה קָנִיתִי בַּהִזְדַּמְּנוּת
We like this word so much, that we even have a verb made of it! A wife could say "if you happen to pass a shop on your way, please buy some buns and shoko for the little one!"
אִם יִזְדַּמֵּן לְךָ לַעֲבֹר בְּמַכֹּלֶת תִּקְנֶה בְּבַקָּשָׁה לְחַמָּנִיּוֹת וְשׁוֹקוֹ לַקָּטָן! And then - well, you better not come home empty-handed. :)