With groceries and meals on my mind, here's something I have found extremely useful! I had this chart when we were in the WIC program (Women, Infants and Children). It made everything so easy when I wanted to buy fruits and vegetables, and it helped me get into the habit of making fresh produce a regular part of our meals. I think I used to imagine it would be so expensive to get all that produce, and it can be, but this chart helps break it down on the cheaper levels, too.
I've put this together to share because it's been something of a life saver for me at the grocery store. I like math, but only when I can sit with paper and pen, not when I have to figure it out in my head or take the time to work it through on a calculator while I'm trying to get groceries.
For your further convenience, here's a copy with just the chart for printing.
I'm keeping mine laminated in my purse.