Can I get some preservatives, please?

I have never borne witness to food that expired so quickly.
Two days ago, I was assaulted by a moldy loaf of bread (I'm slightly terrified of mold). The bread was purchased by a friend less than a week prior, and when she went to the kitchen to fetch it, she returned with something that resembled one of those green styrofoam blocks you stick silk flowers in. I have seen moldy bread before, but this was a whole new class of expired. How could one week cause this much damage?! A carton of milk also managed to expire in under two days, even though it was refrigerated. And jam! This was something I had never seen before in my life. A jar of jam was moldy after no more than ten days. I have jam in my refrigerator at home that has been there for months and it is still good.
I even checked all the expiration dates to make sure I hadn't purchased old food by mistake. But all of the spoiled food was spoiled well before it was expected to expire. I am at a loss. Many more of my purchases have gone bad and I'm sure many more will. But this makes me much more wary of the food at home in the States. How many more chemicals are going into my food than I'm aware of? If food spoils this quickly, what on Earth am I putting into my body at home? Or is it just Poland? Does food just spoil unreasonably fast here for some reason? I would love to know the true factors that come into play in this situation.
I am enjoying the European trend of purchasing fresh food. It's nice not going to Walmart and purchasing bags of frozen vegetables and chicken. However, if I want to make a salad, I have to actually purchase a head of lettuce, a carrot, a jar of olives, an onion....you get the point. I don't really have the option of buying a bag of pre-mixed salad. I am beginning to miss the pre-packaged convenience of certain items, because if I buy a whole head of lettuce, it's going to go to waste. I can't eat a whole head of lettuce in one salad, and as I stated early, everything will be spoiled by the time I am ready to eat more. Even though it seems insignificant, it is actually quite a dilemma. We're on a limited "income," or stipend, here, and I really can't afford to be throwing food away, no matter the amount.
I'm really missing that UNCG meal plan right now....