I'm just starting the Extracurricular Activity scenario. I see there is an Elder Thing effect on the Scenario Card, but the Campaign Setup instructions do not add an Elder Thing token to the chaos bag. I'm going to assume that token might get added at some point during the campaign, but not putting in bag to start. Please chime in if anyone knows differently.

Your assumption is correct. Saying anything more would be spoiling things....

Also each scenario can be played in standalone mode which is usually a bit harder as you can bring whatever do into it as you like and the make-up for standalone chaos bags often has tokens of each type in them.