![2girls age_difference ahoge backpack bag bangs black_hair blush blush_stickers bow breasts clenched_hands clock closed_mouth coat comic ears_visible_through_hair eyebrows_visible_through_hair gift_bag hair_ornament hairpin hamkuti highres knapsack long_hair long_sleeves looking_at_another looking_at_viewer looking_away multicolored multicolored_eyes multiple_girls open_mouth original purple_bow purple_hair randoseru speech_bubble standing translation_request yuri rating:s score:0 post #3449185](/cdn_image/preview/43/eb/43eb2bd721db2421adb6faf2e4d76902.jpg)
Either a small bag made out of fabric that is tied at the top with a ribbon, or a colored paper bag with stringed loops at the top for holding. The bag will contain a gift for one person to give to another as a surprise.
Don't confuse this with a sack, often associated with Christmas and Santa Claus. A sack is one large bag that can carry multiple wrapped gifts, whereas this is a single bag with a gift inside it. An example with both a gift bag and a sack clearly present is post #374610.