For this item you should really stick to the use by date. While you shouldn't keep it for more than five days after opening, use your nose as it will always tell the truth if the milk is off.
Because cheeses are mould it is hard to put a time on the food life of this item, but a general rule is to stick to the use-by date provided on the packet and personal taste.
Butter and margarine
You would think these two have the same life expectancy, but they don't. Butter can last between one to three months and longer if kept in the freezer, but margarine (it's more processed partner in crime) can chill out for up to five months.
If you are not going to eat your meat straightaway chuck it into the freezer as it will keep for much longer. But, if you do plan on eating it make sure you keep it in the fridge for no longer than a week. Salamis and cured meat can be kept for up to a month in an unopened packet. Also ask your butcher to vacuum pack your meat as they will keep for a few weeks longer than regular packaging.
Most condiments should be kept in the fridge for no more than six months, but mayonnaise and other salad dressings will spoil after three months.
Most fresh vegies can keep for up to a week, maybe even longer if you are lucky. While many of us are guilty of keeping our vegies for longer, make sure you do throw out the old ones when they brown or feel limp because the longer you keep them in the fridge the more likely they can contract a food borne illness.
Berries can go off within a few days of being bought, so make sure you pick fresh produce. Other fruits such as melons can last up to a few weeks, but oranges and apples if in season can last up to five weeks.
Make sure you check the use by date on your eggs when you buy them. Generally eggs can last up to five weeks uncooked and can be stored in either the fridge or the cupboard. If you do boil them, they last for 2-3 days in the fridge.
Yoghurt is similar to milk, once opened keep for no longer than two weeks. But make sure you do look at the use by date as it is a good indication of when it will go off.
Leftover dinners should be consumed the next day or within three days of being cooked. If it has been longer throw them out!