Answer:
Cuando voy de viaje, nunca compro regalos.
Explanation:
The sentence "cuando voy de viaje, siempre compro regalos" has a positive adverb of frequency which is "siempre" and means "always" in English. To transform this sentence in a negative sentence you have to change the adverb of frequency "siempre" and instead of using and adverb which means "always" you will use an adverb of frequency that means the opposite, "nunca" which means never.
