AngularJS shopping cart using local storage
This is interesting,

you have quite a bit business logic in your code there..
If I were try to break this, I would definitely change the price of the items I buy in the local storage to 1 cent and see if the server side would accept that price. (It should not, and recalculate any pricing from item master data). Next I would place a breakpoint in some of your btw related routines and make it return 1 cent and see if the server side could be broken that way.

Other than that, I see no security flaws in there. Let me know if you want me to do a review of other aspects of your code.