If you're not getting enough Vitamin D, that's one deficiency that responds well to supplementation rather than dietary changes.

I also only get groceries once a week and so I make a big pot of whatever and put it in single-serve containers - this week I'm making a beef pasta sauce one day and an eggplant and cauliflower curry the next, and that will last all week. When I want a meal, I can either just eat that, or add rice or pasta. Cooked, it all keeps in the fridge for a week with no problems.