I confess, I hadn't a clue Postmates
was a thing until a couplefew months ago. Maybe you aren't familiar with it either.
Basically it's a service where people will deliver things to you. From restaurants to stores, all sorts of places. Fast food! If you've occasionally wished Dairy Queen would deliver, this might be the thing for you (though how well it works may depend on how close the DQ is and how hot it is outside and what you order). The service is available in a bunch of cities, check their website to see if it'll work near you.
Lots of places have menus available in the app (I sometimes wind up checking out the restaurants own websites for more detail if I'm not already familiar with the place). Stores might have a list of frequently purchased items with prices (I know Apple Stores do). You can also request items that aren't listed. Or have them get things from places that don't have such details in their system. I've always just purchased things that were listed so I'm not sure how well it works if you go rogue. ;-p I've had good luck with delivery people for the most part.
When I first used it, it was with a credit worth $100 of delivery fees for a week. So I was able to get things without paying for delivery so stuff just cost what they would at the restaurant/store + whatever I tipped the delivery person. Not a bad deal. That week I went a bit wild and got lunch from various fast food joints most days and that was novel. We're pinching pennies so it's hard for me to justify this when there is a delivery fee, though they do have a limited number of places where there's a set delivery fee that's cheaper than usual. Plus they seem to run deals fairly often where you get free delivery.
When that Unicorn drink was A Thing I remember seeing people using Postmates to get the beverage so they weren't the ones waiting in line but instead it was a Postmates person (one hopes they tipped well if it took a while).
Anyway. I'm mentioning it in case you want to get in on one of those $100 in delivery fee credit for 7 days deals. Use my referrer code of "FZYD2" to get that deal (I'll get a delivery fee credit of up to $10 after your first order). They've been warning me that this deal isn't gonna last much longer, thus my mentioning it. (Sneaky, Postmates. I bet they offer yet another referral deal after this one expires, no idea if it will be better or worse.)