Depending on the size of your laptop you can look into buying a backpack that has a detachable daypack that will fit your computer. Something along the lines of the Farpoint series from Osprey. Or if you don't want to buy a whole new backpack, you can put your computer in a light weight rucksack or gym sack and carry the rucksack in your backpack or with you if checking the main backpack. I do that all the time.