Christmas period is very quiet. Most shops are closed. Coffee shops are still open though.
Surprisingly the town is much more animated at night: woke up at 3am when a group of car tuning dudes were trying out their engines right outside the hotel. They looked like they were preparing for a Fast and Furious night race. There is an active motor racing culture in Kuching. Several cafes have a garage or car racing theme. The best one is Feast and Furious which shows off actual racing cars and motorbikes collected by Alex 'Stmrock' Wong, a local biking fan.
Lots of quirky little cafes. Even in low season people queue up at Black Beans Coffee to buy some freshly ground Sarawak coffee.
If you're into lavish dinner buffets you can find good ones for under MYR100 (SGD30) at the Carvery, the Hilton Waterfront Cafe and the Pullman.
Going to Kuching from Singapore is quick (the flight lasts a bit more than an hour). I paid SGD360 return during the Christmas period when booking 2 days in advance.
Going from the Kuching airport to the city centre by taxi is less than MYR30.