What should I keep in mind while buying foodstuff?

What we eat is what we become. So, one must know what one is eating. The following things must be checked while buying any packaged foodstuff:

Check both the manufacturing and expiry dates. Milk and meat based products have significantly shorter shelf life than vegetable based products. Dry packages have significantly shorter shelf life than moist packages.
Always check the ingredients! The component information can be especially important. For example, one may be allergic to a particular kind of grain used in a foreign dish. Someone may be a vegetarian, and may keep eating non-vegetarian components just because he didn't check the label! Heart patients, diabetics, hypertensives (people having high BP) must avoid food that is high in salt (particularly sodium). All this information can be found on the label. Foodstuff that has its label in a language you don't understand is best avoided, however attractive they may look!
Double check the ingredients! Know that whole grain is better than processed grain. The latter loses its fiber content while processing. Check the preservatives used. If you're in doubt about one of the ingredients, ask the store staff for help. If still in doubt, leave the packet.
Check the Nutrition information given on the label. Note how much calories, fat, and vitamins the packaged food gives. Obese people must avoid high fat food if they are to make a contribution to their health. Vitamin content (particularly vitamin A and B group) should be high, because growing children, pregnant and lactating women, and the elderly need them in more amounts.
Needless to say, check every packet for leaks or tears.
Canned food is especially liable to contamination by anaerobic bacteria. Check if the container appears unusually "stuffy" (under pressure of the gases produced inside by the bacteria). Whenever you open a canned food container, check if it emits bubbles. If so, discard it.
Compare different brands at the market itself. There are tremendous differences in prices, quality, as well as nutritional content among brands. Make a good choice.
Buy a variety of foods rather than large quantities of some chosen foods. The variety helps in giving you all the essential amino acids, essential fatty acids, vitamins and minerals everyone needs. Remember, the food you hate the most has some nutrients no other food has!