Welcome Susannah! I can tell you too are burdened with glorious purpose.
If you run into Loki during your time in
Avengers Campus at Disney California Adventure Park, lucky you! I hope you do, and just in case, come prepared with your best Loki pose and ask for a picture with the God of Mischief himself. While you're in the area, check out
Avengers Headquarters for Character experiences and entertainment and take a look at the showtimes for The Amazing Spider-Man! on the
Disneyland mobile app, which we ended up watching multiple times.
It's really thoughtful of you to want to bring a gift for Loki. While I've seen small Guests bring treasures they'd made for a favorite Character and my children made Valentines, which they handed out to Characters on Valentine's Day, I think you're better off wearing your duck pin and pointing it out to Loki. It will make for a fun point of interaction and Loki won't be put in the position of having to turn down something of value. We all know turning down anything runs contrary to his nature.
While you're in Disney California Adventure Park, check out the
Food & Wine Festival. There are always really yummy offerings at the Festival Marketplaces. I'm sure there will be something fit for a god.
Have a great time!
Elizabeth