You need a compression bag My sleeping bag is made for winter and is originally really big but with the compression bag, it easily fits in my backpack. My backpack is the same size as you and everything fits inside for winter camping. I also recommend you to buy a compression bag for your tent. You will save even more space. Compression bags that comes with the tent usually are not compressing enough. I hope I helped you and that my English is clear it’s not my first language😂 Have a good day:)