Personally, I use total calories + serving counts. My goal is to achieve 2000 calories per day for each adult, and 1000 calories a day for each child. And almost every product has a serving size + total servings listed. You can even look these up with the FDA. Today, they are starting to use actual measurements for servings, but you can convert older serving sizes to actual measurements. So figure out your calorie (& protein) needs (or if you are really picky, also include your salt, potassium, and fat needs) and determine how many servings of foods you like to eat will fit the bill per meal x total meals & snacks per day. I like the idea of 4 servings per meal + 3 meals per day + 2 additional snacks per day. (1 slice of homemade bread is always 1 serving included in each meal for me; so it's really 3 servings + 1 slice of bread) I think this will often achieve my personal 2000 calorie per day goal. And if I plan my meals well, it should also achieve the needed fat & complete protein requirements.
Despite in some cases where I have to use #10 cans, I prefer not to use them as you have to use the food up once opened before it goes bad. When I bought a supply of food that came in the #10 cans, I discovered that for some items, there was only 1 can that was supposed to be used throughout the duration of the food provision time window. It's just not realistic to spread out the food from such a can for long periods of time. How long will a #10 can of powdered margarine need to last one person?, probably a long time. Will it last that long after opening in the summer if no refrigeration is available? Probably not long enough.
However, I think I have found something that will help: Some grocery stores carry zip-lock baggies with vacuum valves in them. They are made to vacu-seal them with either a battery-powered handheld vacuum pump, OR a hand-operated vacuum pump that looks a lot like a small bicycle hand-pump. I like to vacuum seal dry goods for long-term storage, SO I've stocked up with a battery-powered pump, a hand pump, and several bags. Now, when I crack open a #10 can, I use what I need, and vacuum seal the rest with my normal sealer. And if I lose AC power, I'll use the battery-pump. And if I lose my AA battery-12VDC charger-solar panel system I currently use for battery-powered camp items, then I'll break out the hand pump. So, it looks like the #10 can food longevity problem is now solved.