Pre-packing food in portions and in units of 100 calories helps me stay within the calories I need for the day. On busy days I can pack for lunch and breakfast by grabbing my "food units" - 10 items = 1000 cals - I can toss them into my lunch bag and stay within my calorie guidelines!!
I use baggies and reusable 1-cup bowls with screw-on lids. I keep a couple of ice packs in the freezer. If I pack at night I leave my bag in the fridge. If I'm rushing out the door, it takes 5 minutes to pack and I make good choices.