I tend to work for nonprofits like Aspiration that do a lot of events for our constituents. Our goal for each event is to spend as little money as possible on the food by either getting it donated or ordering pizza instead of getting catering.
I found that in my past organizations, we spent a lot of time requesting food donations, doing food set up/clean up as well as errands to pick up things that we ran out of or forgot to get.
When I did the math, I found it was actually the same cost and sometimes cheaper for me to hire a caterer who takes care of all that stuff like set up and clean up. Now with all Aspiration events we hire a caterer. I usually pick one who charges between $15-$18 per person (including tax) for breakfast and lunch combined.
Now that I have the extra time that I don't have to focus on food purchasing or preparation, I focus my attention on the important aspects of the event like posting notes to the event Wiki like http://www.advocacydev.aspirationtech.org and contributing to the sessions.