No business -- large or small -- would ever dream of merging with another without a carefully crafted contract.

If married and unmarried couples took the time to work out contracts for their various unions, there might be less business for the courts.

Basically, there are three types of contracts to fit these specific situations. There's the prenuptial agreement for people contemplating marriage. There's the marriage contract for people who are already married and want to spell out who does what with the business of running the home and bringing up a family. And, then, there's the living-together contract for unmarried people who want to spell out who gets what if there's a split.

Prenuptial contracts are usually drawn up when one of the parties has considerably more wealth than the other. This type of contract is sometimes used by couples marrying after one or both partners lost a spouse through death or divorce.

When a fairly well-off person plans to marry someone less fortunate, the children on the money side might get nervous and sometimes quite vociferous. They don't want "that other person" to get their inheritance.

A prenuptial agreement can be drawn up to soothe the ruffled heirs and still make the other partner not feel like a beggar. Actually, you can't disinherit your new partner. Most state laws specify that a surviving spouse must get a certain minimum percentage of the estate.

Given the high divorce rate, some couples try to draw up prenuptial agreements which spell out who gets what if there is a split. Some states, however, prohibit contracts that detail divorce terms because they feel it might actually encourage divorce.

Some young people who savor their independence try to work out marriage contracts that spell out who does the cooking, who looks after the baby and on down the line. This is a lot of fun and it gets some repressed feelings out on the table where they can be dealt with.

However, this type of domestic duty contract is rarely, if ever, legally enforceable. The courts have studiously stayed clear of getting into domestic duty squabbles.

Finally, there's the living-together contract that, in some ways, imitates the prenuptial agreement. Only in this case the couple is not officially married.

In the much ballyhooed case of Marvin vs. Marvin, the court eventually said unmarried couples could have binding contracts as far as the split of the wealth goes. And, furthermore, these contracts for unmarried couples did not always have to be written (although this type is preferred). They could be verbal or even implied.

Couples who live together should sit down and seriously sort out who owns what and who gets what in case the unmentionable happens. Lawyers advise unmarried couples to keep separate bank accounts, credit accounts and other separate property wherever possible.

Couples may choose to form a joint account to run the home and pay the bills. Each contributes a specific, agreed-upon amount. Then, if anything forces a split, all the property is sorted out according to the contract.

Living-together contracts are particularly important when the couple is planning to buy a home, have a baby or make other major decisions. Getting assistance from a lawyer is advised.

For a set of sample contracts and a step-by-step guide to forming living-together arrnagements, you can get a Living Together Kit, written by lawyers, by sending $8.95 to Nolo Press, 950 Parker St., Berkeley, Calif. 94710.

Q. You can save considerable money by purchasing specials at the supermarket. But when you buy a large amount of canned food, how long can it be stored before it gets bad?

A. Most canned items will stay fresh for about a year. Canned milk has a limit of about six months. Pastas, rice and dried beans can stay unspoiled indefinitely if they're kept in a cool, dry place and they're properly packaged. You can get more information in the free booklet, "Family Food Stockpile for Survival," published by the Agriculture Department. Write Office of Government and Public Affairs, USDA, Washington, D.C. 20250.