The way it worked before was that you could trade in one QS credit for three snack items, in one transaction at one location. To do it, you just pick out three snacks and ask them to charge a QS credit. Some kiosk-type locations weren't eligible.
Whether they will continue that policy in 2024 is unknown, but we'll know more about the changes by May 31, when booking begins for the dining plans.
Keep in mind that packaged snacks in merchandise locations like resort stores and Goofy's Candy Kitchen qualify, so you could get a rice krispy treat, small back of pretzels and chocolate bar, and eat them on the plane flight home, or save them for a treat. And, of course, you don't need to use exactly 2 credits each day. You could save a credit and use it on a later day, like for breakfast, maybe on your checkout day.