I have seen it done B4, but in a very bad way. They used number of cups for inventory of drink sales, thus $1.25 drink also charged $1.25 for empty cup b/c inventory of cups would show a sales loss.
In this new economy, I think you could place a positive spin on a campaign of "Only pay for what you use." This would require more inventory analysis, but could be savings for you and customers (and when customer saves, they come back).
So track cost of cups you pay per pkg. Divide cups per price. Let's say each cup costs you 9 cents so you charge 10 cents a cup (don't be greedy). Now you have set price for 12oz. of drink. If customer brings in container holding 12oz. they only pay the drink price without the 10 cent cup price. Customer gets to feel "green friendly," are pleased with cheaper purchase. Others are aware of 12oz. drink + 10 cent cup price.
This could be done full scale on all products. Meals, plates, utensil, etc.
Again use that positive spin on why pay for utensils if you're bringing food home & have your own flatware, but can buy utensils if you are taking food to park. Price per utensil would be so minute as to not cause problem. That's why I suggest 1 cent over your cost so as not to cause a stir among customers.
Then let them know this experiment to see what customers want. Ask for feedback. Customers like when you ask them how you can serve them better.
Being in Marketing research for 8 years, I learned that customer service beats out price & quality everytime. B/C there is the assumption that any quality problem will be fixed to satisfaction & price can be adjusted because service has shown that dialog is open between you & consumer.
Hope that gives you enough information to help you think on how what may suit your customer needs.