Big fan of this soloman vest 
https://www.salomon.com/en-us/shop/product/adv-skin-12-lc11657.html#color=66310

You can pack it super light with just the bottles (500ml each) or you can throw a full bladder in the back. Combine both and you can get 3L easily. 

Tons of space for phone, snack, jacket, whatever. Just make sure you don't get it too big, otherwise it'll flap around while you run.  

 These vests are great! I  agree wholeheartedly 💜