At Hindu temples, prasadam is food that has been offered to the deity and is then distributed to devotees — a blessing made edible. Accepting and eating prasadam is one of the most direct forms of participation available to a visitor in a Hindu religious context, regardless of your own beliefs.
What is distributed varies by temple and by time of day. At the Ekambaranathar and Kamakshi Amman temples, prasadam is typically a small portion of sweet pongal (rice cooked with jaggery and ghee), coconut pieces, or fruits distributed after the main puja. At the Varadaraja Perumal Temple, the association with the Kanchipuram idli means that rice preparations are sometimes available.
The distribution happens in the outer precincts of the temple after the main morning and evening pujas. You don't need to ask — it's offered to everyone present. Receive it with both hands cupped, eat it on the spot or nearby, and don't refuse it casually. The gesture matters more than the food.
For visitors who want to engage with Kanchipuram's temple culture beyond looking at carvings, taking prasadam is the simplest and most meaningful way to participate.