The literal translation of "dig" into "menggali" doesn't quite do it. To better reflect the meaning in English, the Indonesian translation should be: "Mereka meraih kantong tas mereka".
is it wrong to say: ... dalam kantong tas ...
Why is tasnya incorrect?
"Tasnya" would translate to "her/his/its bag", i.e. singular ownership. I believe the intent here is using "they" meaning multiple people, so the translation would be "tas mereka".
I think the translation is better as: Mereka merogoh kantong tas mereka; not Mereka menggali kantong tas mereka. "Menggali" is more about "making a hole", such as "menggali tanah".