At the higher-end grocery stores near me (Whole Foods, Nugget, etc), you can bring your own container and tare it before filling. Maybe you can see if your local grocery store can do this at the deli/olive bar?
Our local co-op is a lot more streamlined for this, they even do periodical sales for people who bring reusable containers.
Our next goal is to bring our own containers when we eat out, in case we don't finish the food and want to bring the rest home. Often times we purposely order more than we can finish so we get a greater variety of things to share and a whole extra meal the next day.