eating before Mincha, cans and cut veggies

Question

Hi Rabbi, thank you for taking the time to answer my questions. I was wondering about the halacha that one can not start to eat samuch to mincha or maariv, meaning half an hour before mincha [or maariv] - does this mean that once half an hour after chatzos comes i must daven, even beyechidus if i want to eat ? what if my usual minyan is mincha ktana ? what are the exact parameters of this halacha ? i always feel guilty for eating lunch and not trying to daven early. and what about maariv ? do ineed to always daven before supper or can i put it ff for later and just say kriat shma ? also - do canned veggies really need a hechsher- from what i've read of yor posts regarding other things it seems not ,but what of bishul akum ? and what about veggies like carrots that are cut up and bagged ? thank you again.