One great way to Figure out portions is listed in the book "well fed". Check out the link if you're interested.
Well Fed: Paleo Recipes For People Who Love To Eat | theclothesmakethegirl
I second the idea of two trips to the store. On Sunday I make a large portion of meat that I can put on salads or incorporate into stir fries. When I run low I have frozen burgers(organic from Costco) and/or frozen veg. Costco has great options of frozen veggies at a good price. Wednesday or thursday I'll do it again.
Also, meat freezes well. Wrap in plastic or foil and drop it in a ziplock freezer bag. If you make a big portion of meat, freeze half on day one. Then when you run out you can pick out some thing from last week for variety.