Having spent 3 years as a barista in 2 different shops, I can tell you this isn't just saving money, this is cheating and stealing:
DON'T DO IT!
Why? Why is it wrong? Well, look at it from the other side of the counter. Look at it from the point of view of the awful, greedy person taking your hard earned money from you. They don't own the shop. They work for a manager and an owner who has to make money to keep their shop open. As a barista, if you don't up-sell, if you don't bring in the kind of money expected of you, well, you don't necessarily lose your job over it but you do hear about it and occasionally get yelled at. Trust me, hearing the words "Sample! Sample! Sample!" twenty times a day, 6 out of 7 days a week is not something you look forward to.
If you honestly can't afford to spend the kind of money it takes to get your fancy coffee drinks, you can easily do some research online to figure out how to make your favorite drinks at home. Sure, they won't taste just like the drink you get every day at ____insert shop name here____, but neither will your cheater methods. You want a caramel iced latte on the cheap? Buy some sort of dark roast and caramel syrup (Walmart usually carries vanilla, hazelnut, caramel, and raspberry), brew it, chill it, then pour it over ice with milk and add some syrup. It might not taste quite like you want it to, but after some experimenting at home you'll figure out the right combination that you like.
Sure, coffee shops would rather you spend your money at their shop, but I think most baristas would honestly agree we'd rather you figure out a home method than cheat on your drink to save money. Shops don't like that they have to charge you so much and that they're always having to hike their prices (w/ the exception of certain chains). Most independent shops are going to do their best to find ways to keep their prices down and help you out so you don't have to resort to cheating or home-brew methods. Of course, sometimes keeping prices down does mean switching to less costly brands and product changes.
There's also the option of just saving yourself money and trying a different regular drink. Instead of a caramel vanilla latte, anymore I usually get an Americano (typically the second cheapest thing on the menu, regular coffee being the cheapest) or regular iced coffee with a splash of cream. No, it's not as tastey and sweet as my favorite drink, but it saves me money and doesn't cheat anyone.