Before you go into the cathedral and view the event there, put anything you want duplicated (rare equipment, stat seeds, etc.) in your team's inventory, excluding the Hero. You will get second copies of all of these starting after Act 3, which allows for some quite nice equipment combinations and also saves you a fair bit of seed farming.
(As you can see I forgot the part about the Hero's stuff not getting duped. Gonna be farming some Seeds of Skill later...)
Good candidates for this trick:
- Stat seeds/Seeds of Skill as mentioned
- Pep Pips and Pep Pops (you get 5 of the latter when you redeem bonus content)
- Gemma's Charm (forgot this one too)
- Trickster
- Assassin
- Vanguard
- Shield_Bearer
- Warlock
- Belle's Bow
