How to pack check-in stuff

Hello, I'm an amateur backpacker. I'd like to ask which is the best way to pack my rucksack,mat and sleeping bag, before giving them for check-in for a flight. Should I leave space in the rucksack to fit my sleeping bag, or it's fine to give it seperately?

¸íáò ìõóôÞñéïò Üíèñùðïò ïíüìáôé Roarmeister Ýãñáøå :

Thx for the answer. Should I leave unlocked the rucksack too? I was planning to put a 3-digit combination padlock