First of all, these lyrics are poor English! Haha.

Basically, what she means by 'day ones' are the people who have been her friends since the beginning. In other words, friends who have been with her for a very long time, and have remained loyal to her the longest... since 'Day One'. Hope that makes sense?

This is a guess.  Sometimes people refer to ¨day one¨ as when you start something new or start something over, like a new project or a new diet. 

https://www.merriam-webster.com/dictionary/day%20one

So in this context, ¨all my day ones¨ could refer to all the projects she has tried or possibly even all the relationships she has been in.   It could refer to her dreams and failures.

No, it doesn't. In fact, that sentence makes no sense at all.

The only thing I can imagine is that it's a mistake, and that it should be '..all my dear ones'.  That would mean that you are drinking to the health of your family and friends.

Lyrics) They may be really hard to understand...

Raise up a cup up for all my day ones
Two middle fingers for the haters
Life's only getting greater
Straight up from nothing we go
Higher than the highest skyscraper
No Little League, we major
The proof is in the paper

So what did she mean?

Can it be Day One app? 

a simple and elegant journaling app for Mac, iOS, and Apple Watch as ads say

Yes, I agree. A good interpretation.

We don't get to choose 'Best Answer' in Discussions, but Sakib's idea definitely gets our vote.