I try to keep a snack in my purse or car to help ward of temptation when out and about. (The smell of Cinnabons, the free "Hot Now" doughnuts at Krispy Kreme...) The thing two things that seem to work best for me are:
1) Emerald Cocoa Almonds: They come in a one serving size pouch, don't melt and aren't easily squished at the bottom of my purse. (3 net carbs per pack)
2) Atkins Bar: One serving size but very easily squished at the bottom of my purse. A hard eye glasses case is the perfect container for protecting snack bars in purses or backpacks.