Someone gave me a tip on making it a bit sweeter; cut up the fruit you put in, and let it sit overnight. This does seem to work to sweeten it up.

First time I put berries in yogurt, I used blueberries, and it was too sour somehow. I think I'm too used to sugar.

I also often leave my lunch in the car (in the cooler) and I've been using mason jars as lunch containers.