A surf. Rock. Band.

Electric guitarist Isaac K. Brock, multi-instrumentalist Tom Peloso, and multi-instrumentalist Eric Judy collaborated with Shins' lead singer James Mercer (probable payback for Mercer's vocal additions on We Were Dead ...) last spring, apparently adding some grooves to a soon-to-be released and striking surf flick "180 Degrees South".
Chances are the Surf Rock Band From The Land of Plenty aren't going to sound much like Jack Johnson. Probably just a shake of Floyd Rose and a dab of accordian and violin.

Here's a relavant excerpt from the Pitchfork (James Mercer) interview (in lieu of link):

However, one collaboration with another famous indie band that he would talk about was a film soundtrack he worked on with Modest Mouse. It's for the film 180 Degrees South, a documentary by surfing filmmakers the Malloy Brothers. Mercer explained, "Early last spring I went to Chile with a production company that was doing a documentary about a guy who travels to Chile and he runs in with these people who are doing some environmental work down there. So I was invited to come down to Chile while they were filming it because they thought that I might be able to write some music for it. I worked with Isaac Brock on it. We just kind of watched footage after I came back and got inspired and we put together some music."

In addition to Brock, Mercer worked on the soundtrack with Modest Mouse members Plummer, Eric Judy, and Tom Peloso. Mercer described the soundtrack as, "Definitely more soundscapes. I did a lot of acoustic guitar work, Isaac did some electric guitar, Eric Judy has like an accordion thing he was doing and of course playing bass, and then violin." You can hear a snippet of the mostly instrumental soundtrack in the film's trailer here.

Oh, yeah. Interview says Joe "The" Plummer is now a member of The Shins. MM Photog Pat Graham says, however, he's still a member of Modest Mouse. As is Johnny Marr. And Isaac K. Brock.
Full interview if you really want it.