We charged a quarter for ice water because of those cups.
Obviously, my suggestion would be to brink your own drink and lunch to work, but if you don't or you are intending on splurging on eating out at a fast food restaurant, have in your possession a reusable cup. If I remember correctly, we charged $1.29 for soda in our cup, or $.50 to fill your cup. $2.59 for slushies or $1 in your own cup. Now, I obviously don't know if all chains have this policy, but I would take it anyway and ask them how much they would charge. If the teen cashier says "we don't do that", ask for a manager, doesn't hurt to ask.
Just for fun tidbit on my insane frugalness -For our Christmas travel, we had our own drinks in the car, but we decided to eat in the restaurant because of the need to stretch our legs. I was not about to buy drinks off the menu, but I didn't feel right about bringing everyone in their own drink (isn't there the unwritten "no outside drinks" rule in most places?). So I went outside and filled the baby straw sippee cup with a drink and passed it around since no one would tell us we couldn't have a baby sippee cup in there. I couldn't stop giggling at my work around for not paying terribly inflated drink prices. I wonder, do those resteraunts actually ask people to leave for having outside drinks, they're getting some of our money, some is better than none, yes?