I know this probably sounds completely foreign right now, but you are probably not going to have room for snacks for long! Hmmm- Beef jerky (check the ingredients- some have tons of sugar!) Avocados- although, I am not sure if those are as prevalent in London as they are here- I will just eat a half by itself. Get some 70% dark chocolate for "emergencies". I also really like salsa or guacamole: jazzes up raw veg quite a bit. String cheese is good, in a pinch. Tea with stevia and some coconut milk or cream is heavenly. And I love to make kale chips: there are a ton of good recipes online, you can save serious $ making them yourself.