I'm a huge fan of the Nakd bars, this are perfect for putting in your handbag if you find you are getting hungry whilst out. The Cocoa Mint one is perfect for taking away a chocolate craving and the Berry Delight is great for a sweet fix. There are lots of flavours to choose from and they're also wheat, gluten and dairy free. Perfect.
The last option is a savory one. Although i'm not a huge crisp person I find these are perfect if you are needing a salt fix. The Kelloggs Special K Cracker Crisp can be bought in individual packets which are only 86 calories and they don't have a lot of fat in them either. Pop Chips are another brand that do these 'healthy' crisps and I often see them for sale in Starbucks in individual packets, again great to get if you've forgotten to bring something with you.
So those are my go to choices for healthy snacks on the go. My best tip is if you have something healthy in your bag you are less likely to buy an unhealthy option whilst out. Feel free to share some of your healthy snack choices in the comments.