Plan ahead and dress wisely: How to minimise add-on costs when you fly

The business model for many airlines involves charging attractively low prices for the actual ticket, but making customers pay separately for luggage, seat selection and priority boarding.

And it is lucrative: add-on fees, or "ancillary revenue", brings in billions for these airlines every year.

In some cases, passengers find paying the fees is unavoidable, especially if you're flying with children. But here's how to beat some of them.

1. Be ruthless when it comes to packing

There are sometimes bargains to be had when it comes to carry-on bag charges, says Laura Anne Sargeant, who documents her holidays online under the name Travelling Page Turner. But in her experience never anything as low as the £5.99 suggested by easyJet.

"It's usually closer to £20," she says.

easyJet has now been told by the UK's advertising watchdog to stop claiming this price is available, after it failed to provide evidence customers could bring a bag on for that cost.

While budget airlines say they offer low carry-on prices, Which? found in the vast majority of cases they weren't available. The consumer rights organisation only found Ryanair's lowest advertised price (£12) accessible twice out of 634 flights it checked, and found Wizz Air's lowest price of €10 was available twice in 338 flights.

To avoid a bill for carry-on luggage, Laura Anne is "really ruthless" with her packing.

"I'll use the hotel body wash," she says, "I never take a hairdryer."

Then if she is travelling with someone else they can share a case and split the cost between them.

Wendie Smith from Bristol is more of a solo traveller. She is off to south-east Asia for two weeks soon but is only taking a backpack to avoid the charge for putting a bag in the hold.

"It's a soft backpack so it squeezes into their little cages a bit better than a solid one," Wendie said. "And it unzips like a suitcase."

But her best-kept secret?

"Dry robes have massive pockets," she says.

Designed for outdoor swimming fans, these large overcoats can hold a lot of extras and fit over a couple of jumpers.

"They can't tell you what to wear on a plane," Wendie says.

Travel influencer Chelsea Dickenson also loads her pockets with heavier items rather than putting them in a suitcase for the hold.

"Airlines may weigh your bag, they don't weigh you!"

You can even buy vests with many pockets, marketed as a hack that "airlines hate".

If you are taking a bag, the advice is to pay for it as early as possible.

"Prices can increase closer to departure," Chelsea says, "and adding luggage at the airport or gate is almost always the most expensive option."

2. Double check the airline's cabin bag rules

Chelsea warns holidaymakers to watch out for different rules at different airlines, particularly for luggage.

Measure your bag and check the airline's website for precise limits. Don't just go with what your bag claims to be.

"A bag labelled 'cabin size' does not guarantee it meets the airline's rules. Wheels, handles and rigid shells can push bags over the limit."

Helpfully, luggage firms have your back there.

"Companies have got savvy to this and created a whole range of bags where the wheels come off," Chelsea said.

"Wheel your case through the airport but when it comes to boarding, simply take the wheels off, pop them in your pocket and know that you're sorted."

3. Don't fall for sneaky sales tactics

Clicking through the booking process can sometimes make it look as though you have to pay extra to reserve a seat.

But if you do not need a particular seat and you are not bothered about sitting with your travel companions, you can just let the airline allocate you a place.

Laura Anne also thinks paying for priority boarding is "a bit of a con".

Many passengers worry that if they don't pay to board ahead of other people, and then there is no room in the overhead bins for their luggage, they will end up having to pay to put it in the hold.

But Laura Anne says if that happens you will not be charged. You will have to wait longer for your luggage when you land, though.

The booking process is also littered with offers of extra services.

Laura Anne says that while there is sometimes value to be found in booking accommodation or transfers offered through the airline, this is rarely the case with insurance.

"Occasionally you'll find a [cheap] hotel or car hire ... but definitely no to insurance."