Can I just buy clothes there?

Yes. Most major temple sites like Angkor Wat or the Grand Palace sell or rent sarongs at the entrance, but they are often overpriced and synthetic. Buy one locally at a market for a third of the price.

Technically, many strict temples consider form-fitting leggings as 'revealing.' Wear wide-leg trousers or a sarong over the leggings to be safe.

How to Pack Temple-Appropriate Clothing for Southeast Asia

Cover your shoulders and your knees completely to respect local customs at religious sites. Pack lightweight, breathable natural fibers like linen or thin cotton to stay cool while remaining fully covered.

Check the local requirement. Most major temples in Thailand, Cambodia, and Indonesia require shoulders and knees to be covered. Even if it is 95°F (35°C) outside, sleeveless tops and shorts above the knee are universally rejected.
Pack a versatile sarong. Buy or pack one lightweight sarong. You can wrap it around your waist over shorts or leggings to instantly make them temple-appropriate. It also doubles as a light shawl for your shoulders.
Choose the right fabrics. Avoid heavy denim or synthetic polyester blends that trap heat. Choose loose-fitting linen trousers or wide-leg cotton pants that allow airflow.
Select a light top. Pack at least two t-shirts that are not sheer and have sleeves that reach at least the mid-bicep. Avoid tank tops or 'muscle' shirts.
Bring easy-off footwear. You must remove your shoes before entering temple prayer halls. Wear slip-on sandals or shoes that don't require ten minutes of lacing up every time you visit a site.

Can I just buy clothes there?: Yes. Most major temple sites like Angkor Wat or the Grand Palace sell or rent sarongs at the entrance, but they are often overpriced and synthetic. Buy one locally at a market for a third of the price.
Are leggings okay?: Technically, many strict temples consider form-fitting leggings as 'revealing.' Wear wide-leg trousers or a sarong over the leggings to be safe.