It's very variable, some deals are great, some are rubbish, most in between. And it can vary from day to day because it's literally what they have leftover - usually. Though some places basically make you up a meal, Papa Johns used to be on it here years ago and they just cooked you a basic pizza. Don't know why they bothered, and they stopped a while ago so clearly not worth their while!
Good ones in my experience - Krispy Kreme, usually a box of six filled/iced doughnuts and they often throw in another box of glazed as well. Independent bakeries, some round here will give you several loaves of sourdough bread, filled sandwiches, pastries, all sorts. The carvery places, you can pick what you want from what's left at the carvery station. I like the veg and potatoes and sundries best anyway in a roast so not getting much meat doesn't worry me.
Variable - Greggs. Sometimes you get an amazing bag full, other times it's a couple of sausage rolls and a couple of yum yums, neither great when they're not fresh. Starbucks, again sometimes you get a good mix, they seem to work to set guidelines as I'd usually get three savoury things and two sweet. Often it's vegan sandwiches, or a small cheese and marmite sandwich, or a sausage roll, not their most inspiring offerings again it's just what is leftover and needs using so the popular stuff usually sells. Morrisons do groceries and cafe items. Groceries it depends who has picked the bags they can be very full but with lots of stuff like cheap bread and salad items. Hit and miss.
Not great - Costa. Some people seem to do okay but I always got several of the same item, like three cheese and tomato toasties (untoasted) and a croissant. Not a great quantity or variable selection, I've given up with them. Local independent greengrocers, never got a good box from any of them. It's described as being okay for soup or smoothies but I wouldn't want to make soup out of the yellow broccoli and slimy spinach or pick through the really squashed and bruised satsumas and apples. I'm okay with turning spotty bananas into banana bread but much of what I was given was only good for compost.