Don’t you let me catch you throwing out food scraps, no matter how gross they look (or smell). All food is biodegradable and has nutritive value (if only for the compost heap when they’ve gone off) and therefore has no need to be sent to the landfill. I have broken down the wide world of food scraps into five categories: 1) Trimmings, 2) Leftovers, 3) Cooking liquids, 4) Fats, and 5) Steepings (I’ll explain that).
Trimmings. All the little bits you cut off during food prep. I’ll deal only with vegetable trimmings here and address the animal ones under leftovers and fats respectively. You have three options: Most preferably, use them in the kitchen. If the bit was cut off because it was merely ugly (limp, bruised, discolored) and not because it was a potato eye or other inedible defect, toss it in a resealable freezer container and save them up for making stock. A variety of trimmings can actually yield a new plant – such as pineapple and carrot tops, and avocado pits. There are whole books devoted to making interesting houseplants out of used produce. Your second best option is to feed them to your animals. With a few exceptions you can feed any vegetable to any animal that will eat it. Exceptions? Don’t feed very strongly flavored veggies like garlic or onions to chickens, as it will flavor their eggs and meat. Also avoid raw potato peels, which they have a hard time digesting. If you give them any bit of avocado inspect it thoroughly to be sure that it is free of the brown seed covering, which can fatally poison them. If nothing else, you can always have the third option of adding it to the compost heap (or worm bin, if you’re into that). Some things won’t break down in a reasonable amount of time (or ever, it may seem) like peach pits and corn cobs. Corn cobs can also be used as a decent firestarters and as a fuel for bee smokers.
Leftovers. If you’re really good at home economics you can all but engineer these out of your life. I’ve gotten better, but I’m not quite a pro yet. Depending on how much you have left over and what exactly is left over, you can make a new meal out of it in the form of croquettes (leftovers are diced, held together with a thick sauce, breaded, and fried or baked), creamed mixtures (think creamed ham on toast), or croustades and timbales (Cases for forcemeats, creamed mixtures, or other fillings made from stale bread, rice, or noodles. In this instance, both the filling and the case can be leftovers.).  If you have a really small amount of leftover meat or vegetables they can still be chopped up and added to soup, chowders, and salads. Left over or stale breads can also be transformed into stuffing, croutons, sweet or savory bread puddings, meat loaf, and bread crumbs. If the bread has too tough a crust or has begun to turn green, cut off the moldy bit and toss the rest to the chickens, who will fight each other for it. (Daily bread or pasta will make chickens fat, so don’t overdo it. Fat chickens don’t lay as well.) Save any bones for making stock.
Cooking liquids. The murky water left over from sprouting can be fed to houseplants. “Many a drooping coleus has taken a new lease on life after a dose of sprout water.”  Whey, the liquid left over from making cheese, is also the yellowish liquid that naturally separates from your sour cream and yogurt in the fridge. Once separated from its solid counterpart, it can be refrigerated by itself for up to a week before being used in another cooking venture such as a whey-based cheese. You can also add it to soup or stock, make summer coolers with it, use it as the liquid in bread or cracker making, or feed it to pigs or chickens. The liquid you drain out of cans of vegetables or that is left over from cooking vegetables can be added to soups and stock or added to the liquid used to braise a pot roast. But don’t try to reuse the sludge you drain out of commercially canned beans. Waaaayy too much sodium (and probably some sort of preservative). Feed it to the compost. “If the drippings in the bottom of the roasting pan are not used for gravy, chill and add all but the fat to the soup stock.”  Your dog or cat will love you for saving them the liquid from canned meats. I have had good luck with pouring the juice left over from canned fruits (peaches, especially) into iced tea. I usually have about 1/3 cup of thick, sweet liquid left over from one pint jar of home-canned peaches, which I strain and add to roughly a quart of iced tea. The added flavor is generally mild, and you may still need to sweeten the tea with sugar syrup (which dissolves far more readily than granulated sugar). The starchy water left over from boiling potatoes is excellent for bread making. Some folks on Recycle This suggested that pasta water can be added to stock or gravy, used to hydrate grains, and that if you are cooking veggies for the same meal you should cook them first and then do the pasta in that water. If all else fails and it’s a vegetable-based liquid, pour it on the compost heap.
Fats. This includes both the fat you trim off of cuts of meat and the fat in which you fry foods. Uncooked fat trimmings can be saved (in the freezer) for rendering into shortening. Lard (rendered pig fat), tallow (rendered beef fat), chicken, and goose fat all have their own shortening uses; some are best for pie crusts, some make excellent biscuits, some are used for shortening cookies – it’s an article in and of itself. If you don’t cook with the rendered fat you can make soap out of it. Soap is also what we plan to make out of all that strained, used vegetable oil we’ve been saving up. If you’re not feeling like reenacting scenes from Fight Club, you can donate your used cooking oil to a friend who makes biodiesel. If nothing else, you can rub down metal tools with it in between uses to keep them from rusting. Fats and oils can be composted, but (especially in the case of animal fats) I’d recommend burying them in a separate spot than your regular compost pile so that you don’t attract pests and don’t risk contaminating your compost with parasites that could be transferred to your vegetable garden.
Steepings. I made this word up to describe the byproduct of a soaking process in which water is passed through or used to soak a material which is then strained from the resulting infusion and discarded, as is done with coffee grounds, tea leaves, beer mash, cider pomace, and the like. (There’s got to already be a word for that, but I couldn’t find it.) As for coffee grounds – dude, compost that stuff. It’s like black gold for your veggies. If you find yourself in one of those luxurious international corporate chain coffee shops, don’t forget to help yourself to an enormous bag of used grounds on your way out – they frequently keep them right by the front door. I have never grown asparagus myself, but I hear they love coffee grounds even more than most plants. Livestock (especially pigs) love cider pomace. Pomace and mash are both great for the compost bin – but I’ve also heard that beer mash makes killer bread.
 Carrol, Ricki. Home Cheese Making: Recipes for 75 Homemade Cheeses. © 2002 the author. Storey Publishing, LLC.
 Damerow, Gail. Storey’s Guide to Raising Chickens. © 2010, 1995 the author. Storey Publishing, LLC.
 Berolzheimer, Ruth, Ed. The American Woman’s Cook Book. © 1943 Consolidated Book Publishers, Inc.
 Robertson, Laurel; Flinders, Carol; and Godfrey, Bronwen. Laurel’s Kitchen: A Handbook for Vegetarian Cookery and Nutrition. © 1976 Nilgiri Press.