I have studied in Harbin for four years. My personal suggestion:

Get to Harbin before 8 pm on the 31st, and take a taxi directly to the Central Street (9-1 yuan). You can go around the flood control memorial tower by the river, but wear more clothes, and then walk to Sophia Cathedral (go straight south through the underground passage). It's beautiful at night and take pictures. Then you can go shopping in Harbin 1 (usually it will be delayed until 12 o'clock before the festival) or there are more distinctive western restaurants and beer houses nearby, but the consumption is 7-9/ person, and there are hotels nearby, but it is basically 188 yuan, so you can book them online in advance. The next day, you can take a nap and go out around 1 o'clock, and shop near Hongbo Square in nangang district. Yuanda and Songlei are Zhuo Zhan-style shopping malls in Changchun, and the underground is the wholesale place of Shenyang Wuai. Eat nearby at noon, and get full (there is a food street on the right side of Jianshe Shoes City, and there is a roast chicken with a delicious neck, but I don't know if there is any). In the afternoon, take the No.1/No.14 bus and get off at Harbin Institute of Technology and take the No.119 bus to get there directly. It will be dark after playing for a while. It's almost time to play around six o'clock. Take a taxi directly to Long Ta and have a look at the night scene. It's romantic to eat and help yourself (you can book in advance). Then go back to the hotel to sleep, and go to Yabuli Ski Resort the next day (the ticket is about 15 yuan during the festival, so you must book it in advance), and the meal fee is about 5 yuan/person. Go straight back to Changchun after you come back (buy a return ticket in advance, it's very tiring to stand back! )