Getting something "free" causes an unusual spark in a consumer's brain, consumer behaviorists have shown.

That might explain why consumers fill out forms, giving up personal information, for the chance at winning something free in a sweepstakes.

They will diligently clip supermarket coupons and match them to store sales to get a free stick of deodorant. They will act like lunatics on television game shows for the chance at winning free money or prizes.

That makes it all the more odd that consumers nowadays pay for so many things that used to be free. Sometimes, they voluntarily pay.

We pay for TV service, air for our car tires and checked airline luggage. We even pay extra for drinking water. We used to walk or run outdoors; now many pay a fitness center to be a pedestrian on their treadmills.

The point isn't to altogether avoid spending on formerly free stuff; sometimes you have no choice because of marketplace changes.

Rather, the idea is to spend money deliberately, determining whether something is worth paying for. Here's a sampling of stuff we pay for that past generations might not have:

Bottled water. Drinking water is perhaps the perfect example of spending on something that used to be free.

This is a beverage that falls from the sky for free and is available for free at public water fountains.

The cost of tap water at home is so low, averaging one-fifth of a penny per gallon, it's nearly free.

Yet, Americans are spending record amounts of money ($11.1 billion) drinking a record amount of bottled water (9.1 million gallons), according to Beverage Marketing.

The question is, is it worth it to you to buy bottled water, when there is often a free, or nearly free, alternative?

Television service. Adults of a certain age remember when you paid for a television, but the programs were free, beamed to a metal antenna on the roof or atop the TV set.

Receiving free broadcasts over the air is relatively rare now, although you can get excellent high-definition signals that way with the same antennas as a generation ago. Use AntennaWeb (antennaweb.org) to help choose an antenna for your address.

But instead of receiving free broadcast signals, the average subscription TV bill is $86 per month, according to a recent study by research firm NPD Group. Granted, you get many more channels when you pay, and you get no cable stations, such as ESPN, CNN or HBO, when you don't. But the free broadcast networks — ABC, CBS, NBC, et al. — are still among the most watched.

Checking account. Once upon a time, a new bank customer might not only receive free checking at the local bank but also might receive a kitchen toaster as a bonus gift.

Nowadays, you'll be hard-pressed to find free checking at major banks without several strings attached, such as a minimum balance or direct deposit of a paycheck. Fortunately, you can still get truly free checking. However, you might have to switch to a small bank, online bank or credit union.

Use of ATMs used to be free, too. Not so much now. And some banks now charge for the privilege of getting a paper bank statement, instead of an online one.

Checked airline luggage. This one is no fault of consumers. The airline industry refers to it as "unbundling," allowing passengers to pay for only the travel features they want: seat selection, food, checked bags. Consumers, accustomed to those things being baked into the cost of a ticket, just call them extra fees. Typical is $25 for one checked bag traveling one way, or $50 round trip.

Fortunately, you have ways to avoid checked-bag fees, besides overstuffing a carry-on or achieving elite-flier status. For some airlines, you could apply for an airline-branded credit card that will get you free checked bags, although credit cards are inherently dangerous to some spendthrifts, and many cards charge annual fees.

Or you could fly an airline that has no checked-bag fee, such as Southwest Airlines (two bags free) or JetBlue Airways (one bag free).

Tire air. Free air pumps at gasoline service stations used to be common. So was a service-station attendant who would pump the gasoline for you, clean your windshield and check your oil level each time you filled up.

Now with pay-at-the-pump, it's unusual in most states to even interact with another human during the fueling process. And forget about getting free highway maps at the gas station anymore.

For air, you often have to feed quarters into an air pump to fill up tires, which can improve gas mileage by more than 1 mpg, reduce tire wear and possibility of tire failure, according to Consumer Reports.

Auto experts suggest checking your tire pressure regularly. So, it could be worth scouting a station near you that still offers free air. If you're diligent about filling tires, it could pay in the long run to buy your own electric tire-inflation pump. Prices start at about $20.

Of course, some things that used to be expensive are now free. For example, long-distance phone calls were pricey and charged by the minute. Now, unlimited long-distance is a throw-in for service on land lines and wireless phones.

And computer-to-computer voice calling and video conferencing are free with such services as Skype or Apple's FaceTime, as long as you have a fast Internet connection.

Some things have remained free, or already paid for, through the years. Just check out the good stuff at your local public library.

And if you want to give or receive all kinds of free stuff — unwanted lamps, children's bikes, appliances — join The Freecycle Network in your area, via freecycle.org.