I'm so late to this ... I didn't think too much about the peach in that scene, I really just thought it was just Renly taunting Stannis, and, yeah, I guess the peach kinda stands for Highgarden. If it has a further meaning, I really wouldn't know what. I just understood it as a further symbol that Renly was, as Catelyn said, a knight of the summer, who still thought the war was more of a game, nothing to be taken too seriously.
As for Renly coming back ... I want him to come back so he and Stannis can do what they should have done when they met, team up and go BARATHEON BROS BERSERK on the rest of Westeros. I'd love for Renly to come back on way or another and join Team Stannis because he realised that they just hurt themselves and help their enemies if they don't work together. But that's just me loving both Renly and Stannis too much and wanting them to get together and kick everyone's arse. ;) But GRRM being GRRM, I doubt that's going to happen. Also, I'm not sure I want Renly back if he's as much a zombie as Dondarrion and Catelyn.
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As for Renly coming back ... I want him to come back so he and Stannis can do what they should have done when they met, team up and go BARATHEON BROS BERSERK on the rest of Westeros. I'd love for Renly to come back on way or another and join Team Stannis because he realised that they just hurt themselves and help their enemies if they don't work together. But that's just me loving both Renly and Stannis too much and wanting them to get together and kick everyone's arse. ;) But GRRM being GRRM, I doubt that's going to happen. Also, I'm not sure I want Renly back if he's as much a zombie as Dondarrion and Catelyn.