What is a word for something that you always have?

[Nobody ❤]

"For a child milk shouldn't be a luxury but a necessity"

But, milk is already a necessary part of your diet! :| I know it's the opposite of 'luxury' but I feel like a different word belongs here, instead of 'necessity'. It's on the tip of my tongue and super annoying! I can't concentrate on anything right now but trying to think of this word. I can't eat. I can't sleep. I can't study. Please end my suffering and save my education.

What is a word for something that you always have and can take for granted?

HELP

p.s. If you're wondering where this slogan is from, I found it on this fb page:
http://www.facebook.com/MarigoldHLMilkSG

[Cecilia]

I'd use "staple" instead of "necessity" to indicate it's a basic part of your diet.

[otc108]

Why? Why facebook? Why???

[Ghetto]

Synonyms: call cause claim compulsion demand desideratum duressessence essential exaction exigency fundamental godsend imperative indispensability inevitability inexorableness life or death must necessary need fulness no alternative no choice obligation pinch precondition prerequisite privation requirement requisite sine qua non stress undeniability urgency vital part vitals want.


Good Luck

[jiexing tan]

Is it staple?