Well, at least he doesn't have to worry about Kieth stealing it:

To help him get through his grueling live performances, Mick Jagger has an oxygen tank backstage. At 63, the Rolling Stones lead singer struggles to keep his energy levels up for an entire two-hour performance, so when guitarist Keith Richards plays his two solo songs, Mick goes backstage and straps on an oxygen mask.

Because, as we all know, Keith's been dead for about fifteen years now. He looks like they keep him in a shipping trunk between tour stops.