I'm afraid that my experience is that Atkins bars and shakes are very poor. Emergencies only, in my house!
Expensive, stuffed with artificial stuff, and the flavours have been consistently disappointing...
Can you eat nuts?
If so, they make a great snack. and cheese. and olives. and 70% choc solid dark choc, though that is an aquired taste, often. Peanut butter, by the spoon, with a square of dark choc stuck in it like a flake... mmmm
if you need to have something with a long date and a plastic wrapper, then I would go for a mini bag of pork scratchings (I actually prefer these to crisps!) or a 9bar - there are about 6 flavours of 9bar, and I expect we all tolerate the different ingredients differently (some have fruit and carob in them), but I only have a 0.7 mmol/thingy rise with the peanut ones...
ive also been making some low carb biscuits lately - recipe
here, which are incredibly easy.