I wouldn't fret the muffins too much, as post-workout is an ok time to make use of sugars. That said, you could do better. It's not so much what you
are getting from the muffins as much as what you
aren't getting from them. Vitamins, minerals, etc. to replenish your body. Again, this isn't a huge deal immediately post-workout, but it could be valuable.
Dried fruit is the way to go for me. Dates and figs are great. They pack plenty of carbs and minerals (and the mysterious but apparently valuable 'phytonutrients'), and can be easily stored at work or in a sandwich bag. 6-7 dates will give you about 30g of carbohydrates, so you don't need to bring a lot of them. If you have a while before your next shot at some food, go with the figs. They have much more fiber than dates, so you'll have that prolonged release action working for you.
Bananas (loaded with carbs and potassium) would be my next choice.