When the time comes, you will just add enough water to cover the mixture inside plus 1-2 cups more while it cooks. You can add in fresh sliced chicken breast, hamburger, or whatever meat you can find on sale. It's really easy, and cheap to make, and you can make a bunch of it and reuse the containers!
Another thing you can do is go berry picking in the summertime. There is always something wild growing around outside, or crab apples, wild strawberries. Just check out what's close to you or find out by word of mouth. If you are not sure you can always pick something, and have a ranger check it out for you.
In this case, lets say you picked a bunch of wild blueberries and you don't know what to do with them?
Wash them really well. Get a cookie sheet, and put wax paper over the surface. Dump your blueberries on top and try to spread them out as best as you can. Freeze them until they are hard. Grab some of those really good freezer bags, and the blueberries can easily be poured into one since they don't stick to wax paper. It keeps them whole, and unbruised by freezing them this way. You can use this technique for most fruits and vegetables.
You asked what I like to make for snacks.. What don't I like to make for snacks!
I like getting pita bread and cutting it into triangles. I'll drizzle a little olive oil and spices on top, and bake them until they are crisp. You can also mix 1/2 cup wheat flour to a mixing bowl, and add 2 cups of vegetable puree (frozen peas, carrots, squash, potato, etc) some spices to taste (curry is a good one), and bake it until crisp and you've made your own vegetable crisps!
Fresh fruits and veggies are always my favorite snacks. I love ranch and fattening dressings, but a good substitute is buying those salad dressing packets of the dry herbs and seasonings, and adding them to nonfat yogurt. It makes a good substitute for actual salads as well.
If you like cheese, and you can find a big bag of it on sale, get a non stick cookie sheet, and put small mounds of shredded cheese about 2 inches apart from one another, and bake those until melted and crisp. Carb free cheese nips made of all cheese. No flour or chemicals :)
You asked what can be made besides hummus...
Hrmm that's a tough one. Most people like their fattening dips.
I like getting a can of low fat to no fat re fried beans and making my own bean dip with stewed tomatoes, diced jalapenos, lime/lemon to taste, and paprika/Cayenne to taste, with a little low fat cheese thrown in. It's really good warm but can be eaten cold as well.
If you have the time, you can also slow cook beans and make it yourself.
Another thing I like is fresh non to low fat plain yogurt, with chopped garlic or oven roasted garlic, and fresh chopped mint, with kosher salt and black pepper to taste.
As to your last question, about making things approximated as to compared to the store.. That's different for everyone.
When you are cooking stuff from the store (from boxes, cans, bags, etc), Always always always pay attention to the label. The best food has high fiber, low sodium, and low to no carbs. Depending on your diet you want the least amount of sugar too. Many times you can find stuff with sugar alcohol, which is better than regular sugar.
Pay attention to the serving size listed. It will probably seem pretty small, which is why I prefer to cook fresh than from a box.
I've noticed one box of mac and cheese is equal to 4-5 servings. Really?
I know I've probably missed a question or an answer here somewhere, so if I have or you'd like a recipe on anything I mentioned above, just comment and I'll get it up on here. This was a pretty big entry and I know I've missed something!