They were all full of energy when they set out on the trip.
Literal
Trip [to-に] go-out time they [topic-は] all energy-full was.
元気一杯 (full of energy) uses 一杯 (いっぱい, full of) as a suffix. 旅行に出る (to set out on a trip) uses 出る in the sense of departing. みんな (everyone) emphasizes the group's shared enthusiasm.