I believe you can order from multiple people at once.
So you can call up Google express and say "Run by giant, get me a box of ice cream sandwiches. Swing through PetSmart and get me a 40 pound box of cat litter, and while you're at it, my cat is thirsty, so head by Costco and get me a bottle of Kirkland 18-year old Sherry Cask scotch." And, they'll bring it all at once.
Is that right?
Yes, this is true. I can mix my Target order with my Whole Foods order, throw in the dog food from Pet Smart ans it's all delivered by the time I get home from work.
Giant is not available out here, so I can't answer that one specifically, but I'd imagine the Peapod service is similar. You can compare prices with Google Express though...
Also, alcohol is a new addition and I believe it's Northern CA only. For now.