Formal — to staff
Ryokan · Hotel
You
すみません、このお茶菓子（お茶）は持ち帰っても大丈夫ですか？
すみません、このおちゃがし（おちゃ）はもちかえってもだいじょうぶですか？
Excuse me, is it alright to take these tea sweets (or tea bags) home with me?
Romaji: Sumimasen, kono ochagashi (ocha) wa mochikaette mo daijōbu desu ka? / Reply Romaji: Hai, dōzo mochikaeri kudasai. Omeshiagari itadakereba saiwaidesu.
Reply
はい、どうぞお持ち帰りください。お召し上がりいただければ幸いです。
はい、どうぞおもちかえりください。おめしあがりいただければさいわいです。
Yes, please feel free to take them home. We would be delighted if you enjoyed them.
Gesture & etiquette
Pointing at the specific snack/tea, then making a 'take home' gesture (e.g., putting it in an imaginary bag).
Always ask before taking items that are not explicitly labeled as complimentary or souvenir items. Items like bath amenities are usually fine, but snacks or specific decorative items may not be.