So you know for choosing Diamond welcome amenity breakfast:

Breakfast is served at the CenterCourt at level 2.
It covers the grand buffet (hot & cold) items.
or $34 worth value if chosing from the à la carte menu.
More info:
IC Chicago MM : breakfast offering
Garatuities is set $6,12 p.p.
For those wishing something else, there is a starbucks in the hotel off the lobby.
A block away is a good Whole Foods supermarket.
https://www.wholefoodsmarket.com/stores/streeterville