For me, this is how I approach lean living grocery wise-
Lentils- They aren't like beans that need to be soaked and are very versatile. They are also cheap and readily available. Plus, they have an added bonus of being something my very picky husband actually likes.
Mushrooms- They make a better meat stretcher or substitute than some alternatives.
Carrots- Cheap and cheerful and pretty versatile. Carrot soup is one of my favourites, but they are good roasted, in stews, candied, boiled with just a bit of butter and pepper, or filling meats out. You can get a huge bag of these under the "Basic" own brand in Salisbury's for like 18 p. They might not be delicate for salads, but they are fine shredded, and make excellent soup.
EGGS- I can't even begin to explain what a good bargain eggs are. I always buy free-range (usually organic), but even then you can't beat the value.
Fresh herbs- I do the freezing thing too. I also buy some pre-packaged frozen and "lazy" seasoning of things I probably wouldn't buy fresh.
Beans- I noticed a thread where you ask about beans. Get a slow cooker. Don't salt the beans. Soak them for about 12 hours in enough water. Drain. Add fresh water. Cook them in the slow cooker. My MiL gave me a pressure cooker, and they are supposed to cook beans quickly, but I am very afraid of it. It's a "new" one but looks nothing like the new ones. It looks like the old one my nain had and wouldn't let us in the kitchen when it was on the hob. But if you have a new one, they supposedly do beans great.
Onions and garlic- Always have these on hand to spice up dishes.
Lemons- Always at least one or two of these in the fridge.
Spice rack- Red pepper flakes, salt, pepper mill AND preground, curry powder (store bought or homemade), dried herbs, onion powder, garlic powder, dessicated coconut. The "ethnic" section usually has bulk spices much cheaper than the little jars, but spices lose their flavour relatively quickly, so don't delay using them up.
Frozen foods- Not highly processed. Not from questionable sources. Mostly whole fruits, veg, seafood, etc are perfectly fine frozen. Chances are it is fresher than something you buy fresh out of season and was likely allowed to ripen more fully and frozen soon after harvest. Buy fresh and local in season. Buy frozen otherwise. Canned--well, I don't bother with these except canned tomatoes in every season except summer. A tomato in the winter is either a huge impact on the environment, horrible in flavour (if it has any), or both.
Meat-
Look into deliveries. Box schemes can be very reasonable. Even if you don't eat meat at every meal, you can freeze meat for the times you do. Plus, most box schemes use ethically sourced meat. They also sell things like soup bones and cuts you might not find at your supermarket. I recommend the
Well Hung Meat company (they have a nice "thrifty box"), but there are other boxes on offer).
At the market- Cheaper cuts include pork belly (surprisingly good if you slow roast it), POSH sausages (don't bother with the crappy ones, the nice ones are cheap enough), turkey, and slow cooking cuts. Talk to your butcher.
Eat enough fish to balance out the omega 6 you are probably consuming in mass quantities. Eat it a couple of times a week.
Bread-
I don't eat bread normally, but I sometimes bake it. It's not that hard. Trust me. I hate the feel of dough, but it's worth going through the hassle. Some people love bread machines, but I think the bread isn't as nice. My trick is I use a sterilized washing up bowl to mix and knead it. Lessons on bread baking can be found
here. Using the basic ingredients, you know what goes into the bread (and any other baked goods) you make. A lot better than trusting what is put in a mix.
Fats- Don't skimp on the good oils and fats. If you are eating a lot of breads and starches, you probably DON'T need any more Omega 6. Good olive oil. Coconut oil (which has a bonus of being cheap). Butter. Lard, tallow, duck and goose fat. Yeah, I know, you're not supposed to! I am sorry, but millennia of skinny French people can't be wrong. Plus, if you're going to use fats, use them. If you want to cut down on fat, don't substitute highly processed vegetable and seed oils for it.
Along with the library suggestion upthread, I'd suggest you get a cookbook out every week to give you ideas. Focus on basic, traditional foods. Don't be penny-wise and pound foolish with food. Saving money by cutting your food budget to the minimum but eating a lot of floury, starchy, salty, low nutrient foods will cost you in the long run, IMO. You can be thrifty and healthy.
ETA:
http://www.stilltasty.com/ (good guide to shelf life)
http://www.beyondbakedbeans.com/ (focuses on students, but still helpful. I think a lot of it is carby, but YMMV)
There are a tonne of frugal and simple living sites around. Plus, things like the "slow food" and traditional foods movements have a lot of sites about as well. These tend to be less expensive. Plus, there are sites on people's experiences using only local goods or spending a year without buying anything. Finally, you could look into freeganism or more radical lifestyles. You might not decide to go skip diving yourself, but their other tips might help.
Edit to add another thing:
Wine--I forgot this. I always have a moderately decent bottle of red wine on hand to cook with. It helps that I can't drink it, so those who can and do drink red wine might find this more difficult. It really makes a difference in a lot of recipes to add a glug or two of wine.
