It's pretty obvious, but heavyweight items last longer than something more delicate. It also depends how often you wear something.
- A bridle leather briefcase (such as Swaine, Adeney & Brigg). This will take a decade to look great but should keep improving beyond that.
- A shawl-collar cardigan from either pure wool or cashmere. Looks great whatever your age (see Steve McQueen) and is very practical, but being heavyweight if stored correctly off-season...