The problem is that it is hard sometimes to realize that every day you are forced to live paycheck to paycheck or within a box- so it is not so much he doesn't understand the finances, its a matter of learning self control, having the time, and just wishing he had a different taste every now and then other than the same old "sandwich" type thing
Try not to be so hard on him as mad as you are, and I know how you feel, but do things that will minimize his urge to do those things that rob the funds.
Budget quick easy breakfasts,
Make him homemade drinks/lemonade, etc and put in a bottle so he can take with him or keep at work/in the car.
Cook/Prepare meals from the grocery budget that he can grab and go with.
Buy a thermos and keep homemade coffee in it so he can have when he needs it.
I think he just wanted a bit of convenience and didn't have the time or energy to prepare something. He got breakfast once, it tasted good, and he did it again for lunch. I believe you are both on the same page, he just got carried away for once. Just remind him and let it go.