I would have to agree with Rainboe that if you're obsessively picky, or if the issue is so important to you, perhaps you should consider another career path.
Having said that, there's no compulsion to eat the airline food, and yes, you usually may avail yourself of the galley refrigerators. There's probably a lot of LCC pilots reading this that would love to have food of any sort available.
I have a feeling that if you do make it to an airline career, that your 'self-provisioning' will become such a bother, that you will be eating the same muck as everyone else in no time at all.
Regards,
Old Smokey