Remember that the ultimate goal is to keep your insulin low. Spikes are to be avoided, and they're caused by big loads of carbs consumed all at once.
That said, there is lots of room for flexibility. I generally eat about 20g carbs per meal, but I don't worry about the occasional 40-60g carb meal if I'm about to head out for a day of physical labor.
Also, the source of the carbs makes a difference. A can of Pepsi will result in a greater insulin spike than the same number of carbs consumed in the form of steamed veggies with butter, because the fat and fiber in the veggie choice slows the rate of absorption.