I think the more important thing about the "take with food" instruction is to put it separately from the rest of the instructions, so that the patient knows that they have to eat when they take the medicine, not take the medicine every time they eat (depending on the medication and instructions of course).
For example, we had a parent say she ran out of her daughter's prednisolone suspension on the second day, but it was supposed to last for 5 days.
I looked at the script and it was typed as:
Prednisolone 15/5: Take 1 teaspoonful by mouth every day after meals for 5 days
^That's the sig that was typed on the Rx bottle. She was giving her daughter the Prednisolone 3 times a day (breakfast, lunch, dinner).
The hardcopy said: Prednisolone 15/5, 1 ts po qd pc x 5 days, dispense 25 mL
If you read it literally, then the sig on the bottle is correct. However, the proper direction should have been:
Give 1 teaspoonful by mouth once daily for 5 days (give with food)
Give, not take because it's a child, and once daily because the script says qd not tid. Whenever I type scripts that say pc or ac, I always write the "with food" part at the end, and specify exactly how many times a day (once, twice, three times, etc) the med is supposed to be given.
As far as what to eat, unless specified somewhere, most regular meals are ok. Depending on the medicine, eating food can be more to prevent stomach upset than to increase the efficacy of the medication.