Light khaki peasant pants, loose-fitting, possibly linen to enable breathing in humid jungle environment. No belt.
This is one of my favorites, I'll try to get better images of him. The last of the "Blood Island" films shot in the Philippines in 1973. Directed by Eddie Romero and starring John Ashley. And Pam Grier as the Ayesa, the Panther Woman! The Bat-Man is a pretty great effect, done with wires I think. There's also a cel animated version of him which kind of flies into the sunset. Read all about the Blood Island films here.