NEW YORK (CNN/Money) - Your child is heading off to college, and you've devised a plan to pay the big bill.

But as Marc Freedman, a financial planner in Peabody, Mass., says, "Parents usually plan for the expense of college but forget about the discretionary cost during the nine-month period when the child is away."

Read on for suggestions about how to handle those often overlooked but unavoidable expenses.

An estimated 75 percent-to-90 percent of full-time students are covered under their parents' policies, and chances are that's the easiest and best solution for you as well.

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One major exception: if you belong to a closed-network HMO that doesn't provide nonemergency coverage in the school's area. Most other policies will cover children who are full-time students until they reach the age of 23.

Many universities will automatically charge you for health insurance, so be sure to complete a waiver before classes begin if you're keeping your child on your policy.

If you need to make a change, look into the college's plan. "If you've never heard of the insurance company, your antennae ought to go up," said Paul Silva, executive vice president of the Chickering Group, which administers health plans for about 120 schools.

Unusually low premiums may signal inadequate coverage.

Read the fine print, especially the exclusions. Surprisingly, some school plans don't cover injuries sustained in intramural sports. If you need an individual plan, comparison shop at Insure.com or contact a large provider like Blue Cross and Blue Shield.

If your child will be attending a college at least 100 miles away from home and is not taking a car, you may get some relief from the high premiums you've been paying for insuring a young driver.

Some parents see rates go down by as much as 75 percent for the period the student is not at home.

If your kid is taking a car along, your premium could go up or down, depending on where the school is.

David Hargreaves of Argus Insurance in Yakima, Wash., says that one student who was covered under her parents' policy in Yakima for $1,000 a year paid $3,400 for her own policy when she took her car to college in a suburb of Philadelphia.

Be sure to notify your insurer if your child does take the car to college; failure to do so may jeopardize renewal.

Most homeowners policies fully cover personal possessions in dorm rooms, although some have a limit of 10 percent of the value of the policy. If your child lives off campus, you may well have to take out a renters policy, at $100-to-$300 a year.

Caveat: Because laptops are such popular theft targets, not all homeowners policies cover them.

If yours doesn't cover your kid's computer, you have two choices: a rider to your policy for $25-to-$50 a year, or a new policy for $75-to-$100.

Why would you consider paying more for a separate policy? Because making a claim for a lost computer could trigger a higher premium on your homeowners policy.

With book costs for a semester running as much as $1,000, the Web has become invaluable for students.

One example: Buying books (including Homer's Iliad and Euripides' Medea) for the first semester of Literature Humanities, a core freshman course at Columbia University, would cost $120 at full price.

Comparing prices from 21 Web sites at BestBookBuys.com shows that the smartest option is buying used books for a grand total of $54.61, including shipping, from Half.com.

Another option for both buying and selling textbooks: eBay. A new copy of James Stewart's Calculus: Early Transcendentals (fifth edition), which retails for $135.95, was recently trading at $64.

As soon as freshmen set foot on campus, reps from banks will be handing them free T-shirts and key chains as incentives to sign up for credit cards. If your child is 18, you don't need to guarantee a card -- so you don't control which one or ones he or she picks.

The best strategy is to help your kid get a credit card while he's still at home. You can add him to your account, which lets you monitor his spending. Or try a starter card like Citibank's Citi Cash card, a prepaid, reloadable card limited to $1,000, or a student card with a minimal credit limit; Chase's Platinum for Students starts at $500.

If your freshman is among the 76 percent of college students who own a cell phone, a family cell-phone plan may be a better choice than the school's landline offering.

These plans allow you to share minutes and receive one bill. Cingular's family plans, which start at $40 a month, let you add up to three lines for $20 a month each; they also offer rollover minutes.

That's a plus, says LowerMyBills.com's Matt Coffin, because college students tend to make more calls early in the school year.

For students who use the dorm phone but don't sign on to the long-distance plan, get a prepaid phone card. The rechargeable Sam's Club AT&T card (savewithprepaid.com) costs 3.5 cents a minute, plus a one-time $7.79 fee.

Good sites if your child is setting out for a school halfway across the country: Smarterliving.com, which lists travel deals for students, and StudentUniverse.com, which comes up with air, rail and other discount fares when you type in your destination, and lets you book online if your e-mail address ends in .edu.

StudentUniverse excels at last-minute and one-way air fares. In August, a round trip between Boston and Chicago booked 10 days in advance cost $285; the cheapest fare on Orbitz: $410.

A nonstop one-way fare from Boston to Los Angeles was $187 on StudentUniverse; a seat on the same plane cost $1,218 on Travelocity. Southwest Airlines and Midwest Airlines offer student fares; ask when booking. AirTran Airways' Xfares.com allows students ages 18 to 22 to fly standby on any flight that has seats available for $52 a segment (plus tax).