Now, having said crews should be self sufficient I'll give you my theories why feeding fireground crews is critical for more than nutritional reasons!
For one it ensures crews actually stop and have a rest. Also if, as is the case on many, many strike teams, you have not seen much action, the shift is long and boring and the "meal break" aids subtanstially in breaking up the shift.
Also in a lot of cases a meal break, whether on the firegound or at a staging area provides a chance to socialise ("network") with other crews which sometimes results in unexpected and useful operational information changing hands.
If the meal break is back at a staging area other resources can be available - even just someone from another crew who can assist with minor repairs can be invaluable.
Another factor I consider very important (which you may think is trivial) is the fact that the crews actually feel like someone knows and cares that they are there when a meal is organised for them. On Sunday at Ngarkat there were crews calling in regarding meals repeatedly over several hours. I'm sure the increasing frustration with which they requested was as much due to this "care" factor as hunger.