"Meghan usually only carries hand luggage. If she does check a suitcase into the hold it is put on last so it can be located as quickly as possible.
"All the necessary security checks must be carried out in advance or onboard because she walks straight from the plane steps to Harry's car."
Another source claimed that Harry had declined the offer from the airport for Meghan to use the Windsor Suite - where celebrities are escorted directly to their plane by staff - because, at $5,200 a pop, it is "quite expensive".
A Heathrow spokesman said: "The aviation and protective security arrangements of members of the Royal Family, including their movements through the airport, are confidential and fully compliant with regulatory requirements. It would be inappropriate to discuss those arrangements in public."
The news comes as rumours swirl over whether Prince Harry may be preparing to pop the question to his girlfriend of over a year.
Earlier this month Harry took the US actress on a safari to Botswana for her 36th birthday after she flew in from her Toronto home in Canada having filmed the last episode of Suits.
According to reports Meghan plans to move to the UK and give up much of her acting after being introduced to the prince by Soho House director Markus Anderson in London.
Former US marine Kirstie Ennis, a close friend of Harry's, last month said a wedding was on the cards.
Kirstie, 26, whose leg was lost in a helicopter crash in Afghanistan and hopes to compete in the Paralympics, reportedly nodded after journalists asked her whether she'd be going to Harry's "upcoming wedding".
She said: "I don't think I'm worried about the wedding. I'm worried about the after-party."
The 1772 Royal Marriages Act, amended in 2013, means the Queen must consent to the weddings of the first six people in line to the Throne, with Prince Harry being fifth.
Meghan, who divorced film producer husband Trevor Engelson four years ago, will be permitted to marry in the Church of England's Westminster Abbey following the General Synod Ruling of 2002.