I don't use a diabetes-designed case. I just use a small bag and find this works well. Currently, I am using one of these:
To keep things compact, I remove my meter from its case - it's just extra bulk which is not needed if you have a case for everything.
Do you prefer insulation to keep the insulin cool or for protection from knocking? If the latter, I find my pens and meter pretty rugged and can survive a lot of knocks. If to keep the insulin cool, Frio bags are the best for this but they are only needed in warm climates.