We're able to spend about half what we used to on groceries, just by having the luxury of stocking up when we find super good sales. We almost never pay more than $2 per pound for meat, and we freeze it. We buy beans and rice and such in bulk (eating fewer carbs, we're lucky that rice and beans have an almost infinite shelf-life if you store properly).
Soup is my random pantry-raiding standby. It's not only great when supplies are low, it's also perfect for overabundance - when you have leftovers or produce you want to use before it goes bad (in which case I make soup and freeze some).
Most of my soups are "dump" soups. I start with water in a dutch oven or soup pot, add some powdered soup base we buy in bulk (before I found the bulk food store, I used boillon cubes, saltier but still works well). Then I just start randomly throwing in stuff. Leftovers, almost wilted veggies, cans of veggies and/or meat.
My husband (who doesn't cut carbs as much as I do), ha a standby recipe he calls "stuff" (essentially homemade hamburger helper) which is ground beef or leftover meat (diced chicken,ham or roast) browned with diced onion and other seasonings mixed with either rice or pasta and vegetables. The vegetables can fresh, frozen, canned or leftover - whatever we've got.
I make a lower-cab version by eliminating the rice or pasta, to make a sloppy joe style "stuff" that I'll pour over faux mashed potatoes (mostly cauliflower with just a few tablespoons of mashed potato flakes to give it a more potato flavor and texture for very few extra carbs/calories). Or if I want to spend my daily carb budget on a baked potato, I'll pour the stuff over that. Or I'll add beans to the stuff for a chili-like concoction.
Scrambled eggs are another stand-by when choices and time are limited. Like my soups and stuff, almost anything (except fruit) can find it's way into my scrambled eggs. I call them "scrambled omelettes" because I don't have the patience or dexterity to make a traditional omelette. I just saute filling ingredients and pour beaten eggs over it and stir as it cooks. Some ingredients do color the eggs, so if you're really sensitive to color, you have to think about your choices. For example, I once used refried beans and other leftover taco ingredients in a scrambled omelette and the flavor was awesome, but the grayish-appearance was less than appetizing. I wouldn't make it for guests, but it was so yummy I didn't mind.