Whatever you do, don't buy at the airport these items you forgot to pack.

No matter how carefully you plan for your holiday, you will invariably forget something. That’s just science.

Odds are it will be something unexciting, but essential, like your toothbrush. Or your bathing suit.

Picking up another one at the airport is no big deal though, right? After all, why else would they have all those conveniently placed shops?

TO TAKE YOUR MONEY. OBVIOUSLY.

Airport shops have a monopoly on the market. They can charge outrageous prices for ordinary things because they know that you, traveller, are cashed up for your holiday and at least an hour and a security check away from the nearest convenience store.

Of course, some items will cost about the same as in the outside world, but on average the cost of basic travel essentials inside the domestic airport have been hitched up a whopping 61 PER CENT.

The folks over at Australia’s most visited comparison site finder.com.au crunched the numbers for us, and sent through a list of items you'd be better of buying when you arrive at your destination.

Toothbrushes and facial cleanses were actually the best things to forget, with little pricing difference. In fact, one toothbrush was actually cheaper inside the airport.

Unfortunately you'll be brushing without toothpaste though, which was among the biggest airport rip offs, along with was Panadol and power adapters.

You can read the full breakdown based on supermarket prices (left) vs Melbourne domestic airport (right) below:

Toothbrush (Colgate Zig Zag single) $3.30 vs $2

Toothpaste (Colgate Total toothpaste) $3.85 vs $7.95

Deodorant (Dove Original Anti-Perspirant Roll On) $4.24 vs $6.95

Face wash (Neutrogena Deep Clean Foaming Face Cleanser) $15.62 vs $15.95

Panadol tablets 20 pack $3.85 vs $8.75

Bandaids (Band-Aid Fabric Strips) $3.29 vs $5.95

Bottled water (Cool Ridge 600ml) $2.37 vs $4.20

iPhone charger (Buddee iPhone wall charger) $24.95 vs $29.99

Power adaptor pack (Go Travel worldwide adaptor pack) $32.96 vs $69.95

Finder.com.au's resident money expert, Bessie Hassan, also gave Mamamia a few handy hints for saving in while in transit.

"We all know food at the airport and meals on low-cost carriers can be expensive," she said.

"To pinch a few pennies, bring your own instant noodles and tea bags, then all you need is hot water."

Hassan also suggested bringing pre-packed snacks from your pantry.

"The key here is to pack dry snacks - think nuts, muesli bars and chips," she said.

"If you have kids, set aside a few nibbles to whip out pre-landing to make their ears pop."

Her other tips included making sure your cosmetics have lids so they're not taken off you by security, and carrying an empty bottle to fill up with water for your flight.

via GIPHY

Save that money for your first beachside mojito, basically.