alt Hacker Newsin korea u can literally leave ur wallet, laptop, expensive bag at your table and go eat lunch or do something else for an hr and come back and it'll still be there (and people are used to it). one of the few places that surprised me more than japan lol.
but dont leave ur bike or umbrella out.
South Korea has CCTVs all over the place (especially in the cities), and even small-scale robbery is treated as a very serious crime that often it's not worth the risk.