Jurors in the trial of Constance Marten have been shown CCTV footage which appears to show a woman, alleged to be the aristocrat, filling up a bottle with petrol.
Footage also shows the hooded woman, alleged to be the 36-year-old, buying drinks and sweets while at the petrol station on 12 January last year, while living "off grid" with her newborn daughter.
Marten, a wealthy aristocrat, and Mark Gordon, 49, are on trial accused of the manslaughter of their newborn daughter Victoria.
It is alleged the couple travelled across England in taxis and lived in a tent on the South Downs in a bid to keep the baby, after four other children were taken into care.
They were arrested in East Sussex on 27 February last year and, days later, Victoria's body was found in a Lidl supermarket bag covered in rubbish in a disused shed.
The defendants, who deny manslaughter by gross negligence between 4 January and 27 February last year, are on trial at the Old Bailey in London.
They are also charged with perverting the course of justice, concealing the birth of a child, child cruelty and causing or allowing the death of a child.
On Monday, jurors in the trial were shown footage, showing a woman, alleged to be Marten, using cash to buy items including Coca-Cola, Haribo sweets, Mini Cheddars, and matches.
Footage also appears to show the same woman filling a bottle with fuel from a petrol pump.
'Crying baby woke me up'
On Monday, the court heard from Seaford resident Sarah Hidden, who said she heard a baby crying in the middle of the night on two consecutive nights last January.
Days later, she was out walking her dog on a coastal path when she thought she saw the couple she had seen on the news.
Mrs Hidden said: "A couple of nights before I saw the couple, there was the sound of a baby crying. I was asleep but the crying woke me up."
Speaking about hearing the noise for a second night, she said: "It was definitely a young baby crying.
"It's a different sound to an older baby crying, more constant, a bit more high-pitched, urgent sounding."
Mrs Hidden told jurors that she saw the couple on a coastal path sometime between last January 16 and 27, when she took her dog for a walk.
She said the woman "seemed laden down with things", including bags and something on her shoulder.
"My instinct was it was a small baby, but I did not see a baby. I do not remember seeing a head or legs. It was the position you would hold one but it could have been another bag," she said.
Mrs Hidden told jurors she thought they were the missing people she had seen on the news and did a "double take".
She also told the court she twice saw a tent in the area.
Last week, Pauline Mason told jurors that she had seen a man with a woman carrying a lifeless baby in a sling in Stanmer Park in Brighton on 19 February.
Mrs Mason, who had been in a mobility scooter, had described the baby being very pale with her head "wobbling", "floppy" and "unsteady".
On Monday, her husband of 55 years told jurors that she had insisted on telling police about the alleged sighting because she had failed to make a report about the Babes in the Wood murders of two girls in Brighton years before.
Michael Mason said his wife had reminded him about seeing a tent during their outing to Stanmer Park.
The Old Bailey trial continues.