A bracha mezonot is said on certain types of foods. You snacked on cake, muffin, donut and brownies. You make one bracha for all. You don’t make an after bracha, if it didn’t equal a kezyis/approx. half an eggs worth. This is clear. Does it make sense to calculate all the bites of each cake, muffin, donut and brownies and consider it as a half an eggs worth all together? Ultimately, reciting the after bracha: Al Hamichya. Thank you.
You are correct. We will include all of the food that is mezonos to get 1 ounce worth of cake, muffin etc., and then you can say Al Hamichya. By the way if you will take a bit from each of these you will surely have a kzayis, as long as you ate the kzayis within the specified amount of time.