Several comments:
First, like several others, I agree that you're not realistic in your budget vs. your must-haves. It's like saying, "I want to stick to McDonald's prices, but I expect to get Outback Steakhouse food." Yeah, you might manage it on occasion -- maybe the week that your boss gives you a restaurant gift card as a bonus, or the week that you happen to have a buy-one-get-one-free entree -- but you're not going to manage it on a regular basis.
I understand certain things on which you just won't compromise. For example, I only like Diet Coke -- Diet Pepsi can be free, and I won't carry it out of the store. I wouldn't buy Kraft Singles (which are all oil and not real cheese at all) or shredded cheese (do you know why that stuff doesn't behave like home-shredded cheese? The answer is disgusting) on a bet. But I'm also not trying to stick to $100/week. TRY the other brands, see if they're acceptable. If you find yourself REQUIRING more than maybe 5 specific brands, you might need to have a come-to-Jesus-meeting with yourself. If you have a whole bunch of must-haves, you're being too picky.
Next, I would've bought the coffee (well, if I drank coffee). It's a product that you're going to want next week and the next week and the next week, and it would've cost more later. But I would've done what you did -- I would've only bought two packages. I wouldn't have filled the shelf.
Now, my suggestions for lowering your grocery bill. Mine don't always match everyone else's:
The grocery store is an expensive place to buy food. You're paying for the convenience of having everything in one big store, having carts and bags ready for your convenience. Instead, search out other venues. You can find either cheaper food OR better quality for the same cost.
For example, I make a quick trip to the farmer's market almost every Saturday morning in spring, summer, and fall. We enjoy the fresh vegetables, and although the cost is only slightly lower, the quality is immensely better. Sometimes we get great deals: We're
just finishing off the salsa I canned last summer, and the tomatoes for ALL those jars cost me $13 (that wasn't my total cost, of course: I also bought peppers, onions, and limes at the grocery store). I LOVE the fresh basil so much that this year I'm growing a pot-ful at home.
I buy all my spices at an expensive health food store (I don't buy much else there -- most of their stuff is sky-high!). It's bulk spices, so I measure out exactly how much I want, and the amount that'd be in one of those little jars that'd cost $4-5 at the grocery store costs about fifty cents. The store is quite far from my house, so I keep a list inside my cabinet and when I'm going to that area anyway I stop in and pick up what I need.
One of the best things I do to save money on groceries is to shop at a surplus store. They buy up overstocks, food with damaged packaging, etc. Meat is almost always $1.50/pound (it's mostly things like chicken patties that were bound for fast food restaurants, but I do find things like roasts on a regular basis too). French fries are always 10 lbs for $1. You never quite know what you're going to find, but I always find something. For example, not long ago I got a #10 can of black beans, which we enjoyed as black bean soup and in burritos.
Finally, I frequent a new butcher shop that's actually quite expensive, BUT they have great sales. For example, on Saturdays they have ground beef for $1.99/pound with any other purchase. So I'll buy a couple nice steaks and then stock up on the ground beef too.
Another example: We eat LOTS of peanut butter in our house.
Walmart sells a HUGE container -- is it six pounds? -- for around $8.50 for Peter Pan. I can't buy the cheapest store brand for that price, and Peter Pan is one of the brands we like. I do transfer it over to a smaller container because it's easier to serve.
When you do find a good bargain, buy a reasonable amount and fill your freezer or shelves. You should start keeping a price book so you'll recognize the best price when you see it, and you'll start to develop a feel for how far apart sales are going to be. For example, if you learn that a certain store puts chicken on sale every six-weeks, you don't need to buy six-months worth. Once you can predict the sales, you'll know how to shop most efficiently.
In all likelihood, my super-savings places won't resemble what you can find -- but if you look around, you'll find SOMETHING near your area. It might be an ethnic food store or a fish market, but search out your options. Then, because you don't have all day long to shop for food, when you go to these places, stock up on the things they offer for a good price.
Next big tip: Slash your beverage budget. The typical family spends 30% of its food budget on drinks, most of which offer no nutrition, many of which are actually bad for the body. It's hard to justify bottled water, individual sodas or Gatorades, and alcohol when you're trying to stick to a budget. Water is free. Iced tea is almost free.
You mentioned homemade lattes are something like .85 instead of $4 Starbuck's versions. That's a rationalization. You don't need either one. So it's not saving $3.15 -- it's spending .85.
Seek out cheaper meals. You're spending lots on those splurge meals, and that's okay once in a while, but it sounds like you're going overboard on them. Perhaps you should make a rule that for every splurge meal you buy, you must buy a super-cheap meal. Being Southern, we love pinto beans and cornbread. A bag of dried beans costs $1 and will feed my family of four for TWO MEALS. Popcorn is a super-cheap snack. A cake mix (look for them buy-one-get-one-free and they'll be around .50) will make two dozen cupcakes; that's about the cheapest baked good you can have. It seems that most people these days reach for boneless, skinless chicken automatically. Look for chicken thighs; we love them, and they're about 1/3 the cost of breasts. Or, when you do want to cook breasts, slice them thinly instead of serving each person a whole one. Or, buy the large 2-lb bags instead of the little flat packages. Soup is
essentially free; freeze your little-bit-of-this-little-bit-of-that in a ziplock, and then when your bag's full, you have soup -- add in a can of tomatoes, or some rice or barley.
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Brand loyalty - You're right. I will compromise on some things, but not all things. In most cases, the things I won't compromise on are because the brand I buy now is healthier, which is the whole point of eating... to provide nutrition.
I'm so sorry, that must have been such a difficult environment to grow up in! 
