Riou (aka Hero 2): A brand new sparkling pair of bladed tonfa (like the one Talim uses in Soul Calibur), because his old wooden tonfa really got beat up to hell and back during the Dunan Unification War.
Nanami: Book: "Recipes to become a better cook". You know your cooking is bad when the reason anyone can eat it is that he has developed an immunity to it.
Jowy: Maybe some PTSD therapy along with Riou (assuming he would even need that).
S2 Trio: A visit to the Grasslands and the Budehuc Castle. In the Grasslands, they could find Lucia in the Karaya Clan and have an interesting discussion together (but wait, she went to Dunan after S3, so...).
In Budehuc Castle, the trio can exchange martial arts moves with Juan and Emily, Nanami could learn a thing or two about cooking from Mamie, Sanae (daughter of Freed and Yoshino), and (I forgot the name of that male chef); and it's near Harmonia so Jowy could see Jillia (whether she really is Queen or not) and an already grown-up Pilika (she would be around her early 20s by S3) if given the chance.
OT: So, the S2 Golden Trio vs Juan, Emily and Cecile. Which side do you think will win?