My little idea:
Freeze those left over things in ice cube trays so that 1) you don't waste any and 2) you have smaller portions for next time.
Things I love to do this with:
* spaghetti or tomato sauce (especially because I love ravioli with all my heart and when I just make a bowl for myself, I need a little sauce . . . not a whole can.)
* baby cereals (It's super-easy to grind rice and oats to make your own [and save a TON of money, btw] but a bit time consuming to make it up every time, so I just make a moderate size batch and freeze it. For my 4-month-old, the portion sizes are perfect.)
*fresh herbs in water
* pureed pumpkin (or any vegetable/fruit!)
****UPDATED*** Plain Greek Yogurt - It can be used as a substitute for sour cream in so many recipes. But I buy a big tub and then forget to use it! Problem solved--into an ice cube tray, into the freezer, ta da! AND when Squishy gets old enough to eat yogurt with his baby food...easy to add into the mix.