Stones started all three games alongside Harry Maguire as England topped Group B, but Southgate has made full use of his substitutes and shuffled his starting line-up against Wales.
Marcus Rashford and Foden both got their first starts in the third group game against Wales with Rashford bagging two goals and Foden one, and there have been public calls for both to retain their places against African champions Senegal.
Southgate also gave first starts of the tournament to Kyle Walker and Jordan Henderson in the victory over Wales and has an enviable array of options in a squad full of depth.
"The hardest part of being a manager is picking that starting 11. There are 11 happy players and the rest that don't play aren't happy," Manchester City's Stones told reporters at England's training camp on Friday.
"We've got an incredible group here and those that come on from the bench have made big impacts.
"Those players not in the team or coming off the bench have been extremely selfless, they put the team before themselves and sacrifice themselves for the team."
Foden is regarded as the most naturally gifted England ball-player since Paul Gascoigne, and Stones was clear about what his Manchester City club mate brings to the table.
"It is the freedom in how he plays and how he expresses himself," Stones said. "It is frightening. I am a huge fan of him. I am lucky to play with him every day.
"I am lucky, Man City are lucky and England are lucky. I hope he gets what he needs on and off the pitch to help him play like he did the other night."
England will go into the clash against Senegal as firm favourites. They have faced African opposition seven times in World Cup and have never lost.
But in a tournament of shocks, Stones says there is no chance they will underestimate Senegal.
"It does focus our minds. It is the best competition in the world, that is why we've seen big upsets," he said.
"We definitely don't want to be one of those that takes anything for granted and doesn't respect the opposition in whatever form. We've always shown teams respect, no matter what form they've got or players they've got."
