Ethics of spending research money on food and meetings
There are many events one might hold to benefit a particular research effort, for which it is usual to provide at least coffee, fruit, and pastries (at least at my school), sometimes more:


You invite a researcher to visit your university and give a talk about his latest work, which is directly related to, and will help bootstrap, your funded research.
A major goal defined in your grant is to publicize a particular bit of research. You hold an open house and invite visitors from industry and academia to disseminate the results of your research. 
A goal of your research is to develop certain tools and methods and then publicize them. You hold a workshop or "summer camp" for grad students from other universities to teach them how to use the methods/tools you've developed for your research and get their feedback.
You have a collaborator at another location working on this research effort with you. He visits your university once a year for a project meeting, including lunch.


Depending on the nature of the project and the funding, one or more of these may be an  appropriate use of funds. Generally, to be permissible, it must be for an event that directly contributes to the goals of a specific research effort (not e.g. a department event). Sometimes, the grant is given explicitly to host such an event (such as a workshop or summer camp).

(Obviously: follow the rules from the university and the funding source about how the money may be spent. The NSF, for example, has very specific guidelines on the subject.)