John Lennon had been involved in a car accident in Scotland and would miss the first official week of sessions for the album. So Paul, George and Ringo convened at the studio on July 2nd, 1969 to record the basic track for Golden Slumbers/Carry That Weight (both of these songs were connected right from the start) with Paul singing a guide vocal and playing piano, Ringo playing drums and George playing bass. A listen to a bootleg of this basic track shows that the song cuts off immediately at the point where it would be joined to The End, making it quite clear that Paul already had a good chunk of the medley worked out in his mind.
Takes thirteen and fifteen were combined (there were only fifteen total takes) to form the basis for the master. On July 3rd and 4th, George overdubbed his lead guitar and Paul added a rhythm guitar part plus his lead vocal. Paul, George and Ringo then gathered around a microphone to record the rousing chorus.
On July 30th and 31st, additional vocals were recorded, this time including John (this was his only contribution to the song). Also on the 31st, more drums were added to the mix, as well as a timpani overdub played by either Ringo or Paul. The final touch came on August 15th when a thirty piece orchestra conducted by George Martin completed the work. His arrangement encompassed all three of the final songs of the medley - Golden Slumbers, Carry That Weight and The End.
Though the tensions within the group were extremely high during this period, they worked together as well as ever throughout the July and August sessions for Abbey Road. And the fact that all four Beatles agreed to sing the phrase "you're gonna carry that weight a long time" displays a remarkable self-awareness of what the future would hold for each of them.