Having been a volunteer...and casual observer of a ride organized by members of my cycling club, maybe these suggestions will help.

Re: Volunteers
Have you thought about contacting student groups at UT? Depending on when the ride is scheduled to happen, you may have a good source of volunteers there. The coordinator of the Tri County Hill Hopper (Feb, Round Top) works at Texas A&M and is always able to get student groups to volunteer for the aid stations.

Re: Food
I'm not sure if this would fly, but what about contacting some of the Austin Co-ops (thinking Wheatsville), Central Market, or Whole Foods? I think Whole Foods donated a bunch of organic energy bars to the Hill Hopper two years ago.

Good luck!