Prunes are the MVP for regularity
I was advised by two doctors to eat more fiber. One said consume more metamucil. That didn't help much. The other said consume more natural fiber. As I experimented with different kinds of fiber, I found that 6 dried prunes, eaten as is, helped the most along with eating an apple a day and some high fiber whole grain cereal with ground up flax seeds sprinkled on it. Haven't had any regularity issues in the past few months.
Going away for a few days? Make sure you take a bag of dried prunes. Easy to get through the screeners at the airport. If you can't get the other fiber rich food, double your consumption of prunes.