A new 12-sided £1 coin enters circulation on Tuesday, as it starts to edge out the old "round pound" after more than 30 years.
The new coin has been described as the most secure coin in the world and boasts high-tech features, including a hologram.
But consumers craving a snack or trying to park may face confusion when they attempt to pay at coin-operated machines, as some will not immediately accept the new coin. They may find themselves rifling through their wallets for an old round pound.
Tesco trolleys across many of its stores will be unlocked as the supermarket giant performs upgrades so that they can accept the new coin.
A Tesco spokesman said last week that "fewer than 200" of its stores will be affected.
He said last week: "We will continue to have colleagues on hand to attend trolleys in our stores, so our customers aren't affected by the changes."
The old coin and the new coin will co-exist together for a period of around six months, until the round pound ceases to be legal tender on October 15.
The new coins have been made at the Royal Mint in Llantrisant, South Wales, at a rate of three million per day.
They have a gold-coloured outer ring and a silver-coloured inner ring and are based on the design of the old 12-sided threepenny bit, which went out of circulation in 1971.
It might take a few days or weeks for people to start seeing the new £1 coins turn up in their change as they gradually filter into general use.
The Automatic Vending Association (AVA) estimates that when the new coin goes into circulation, around 85% of vending machines will be able to accept the new £1 coin and all will still accept the old coin.
It said that with around half a million vending machines across the UK, ensuring all of them are upgraded is a "major operation".
The body has estimated that all vending machines will be fully upgraded by the end of the transition period on October 15.
Jonathan Hart, chief executive of the AVA, said the upgrades needed for the new £1 coin will cost the vending industry an estimated £32 million.
He said: "We support the Royal Mint and the Treasury's actions to protect the integrity of currency in the UK and reduce the level of fake coins in operation."
A spokesman for the British Parking Association (BPA) said the majority of parking machines will be ready but some older machines may not be able to be upgraded and so new equipment may need to be invested in.
A statement from the BPA said parking machine manufacturers "say they are positive they will be able to manage the upgrade in a timely manner".
One pound coins were first launched on April 21 1983 to replace £1 notes. The Royal Mint has produced more than two billion round pound coins since that time.
The production of the new coins follows concerns about round pounds being vulnerable to sophisticated counterfeiters. Around one in every 30 £1 coins in people's change in recent years has been fake.
The Government has previously described the new coin as "harder to counterfeit than ever before".
People have been urged to return their old round pounds before they eventually lose their legal tender status. They can bank them or spend them.
Around £1.3 billion worth of coins are stored in savings jars across the country, and the current £1 coin is thought to account for nearly a third of these.